查找字符串中字符的最后一个索引-yiteyi-C++库

给定一个字符串str和一个字符x，在str中找到x的最后一个索引。 例如：

null

Input : str = "geeks", x = 'e'Output : 2Last index of 'e' in "geeks" is: 2 Input : str = "Hello world!", x = 'o'Output : 7Last index of 'o' is: 7

建议：请在“上解决” 实践 “首先，在讨论解决方案之前。

方法1（简单：从左开始遍历）： 从左到右遍历给定字符串，并在x与当前字符匹配时不断更新索引。

C++

                         // CPP program to find last index of                       
                         // character x in given string.                       
                         #include <iostream>                       
                         using                                     namespace                                     std;                       
           
                         // Returns last index of x if it is present.                       
                         // Else returns -1.                       
                         int                                     findLastIndex(string& str,                                     char                                     x)                       
                         {                       
                                                 int                                     index = -1;                       
                                                 for                                     (                                     int                                     i = 0; i < str.length(); i++)                       
                                                 if                                     (str[i] == x)                       
                                                 index = i;                       
                                                 return                                     index;                       
                         }                       
           
                         // Driver code                       
                         int                                     main()                       
                         {                       
                                                 // String in which char is to be found                       
                                                 string str =                                     "geeksforgeeks"                                     ;                       
           
                                                 // char whose index is to be found                       
                                                 char                                     x =                                     'e'                                     ;                       
                                                 int                                     index = findLastIndex(str, x);                       
                                                 if                                     (index == -1)                       
                                                 cout <<                                     "Character not found"                                     ;                       
                                                 else                       
                                                 cout <<                                     "Last index is "                                     << index;                       
                                                 return                                     0;                       
                         }                       

JAVA

                         // Java program to find last index                       
                         // of character x in given string.                       
                         import                                     java.io.*;                       
           
                         class                                     GFG {                       
                                   
                         // Returns last index of x if                       
                         // it is present Else returns -1.                       
                         static                                     int                                     findLastIndex(String str, Character x)                       
                         {                       
                                                 int                                     index = -                                     1                                     ;                       
                                                 for                                     (                                     int                                     i =                                     0                                     ; i < str.length(); i++)                       
                                                 if                                     (str.charAt(i) == x)                       
                                                 index = i;                       
                                                 return                                     index;                       
                         }                       
                                   
                         // Driver code                       
                         public                                     static                                     void                                     main(String[] args)                       
                         {                       
                                                 // String in which char is to be found                       
                                                 String str =                                     "geeksforgeeks"                                     ;                       
           
                                                 // char whose index is to be found                       
                                                 Character x =                                     'e'                                     ;                       
           
                                                 int                                     index = findLastIndex(str, x);                       
                                                 if                                     (index == -                                     1                                     )                       
                                                 System.out.println(                                     "Character not found"                                     );                       
                                                 else                       
                                                 System.out.println(                                     "Last index is "                                     + index);                       
                         }                       
                         }                       
           
                         /* This code is contributed by Prerna Saini */                       

Python3

                         # A Python program to find last                       
                         # index of character x in given                       
                         # string.                       
           
                         # Returns last index of x if it                       
                         # is present. Else returns -1.                       
                         def                                     findLastIndex(                                     str                                     , x):                       
                                                 index                                     =                                     -                                     1                       
                                                 for                                     i                                     in                                     range                                     (                                     0                                     ,                                     len                                     (                                     str                                     )):                       
                                                 if                                     str                                     [i]                                     =                                     =                                     x:                       
                                                 index                                     =                                     i                       
                                                 return                                     index                       
           
                         # Driver program                       
           
                         # String in which char is to be found                       
                         str                                     =                                     "geeksforgeeks"                       
           
                         # char whose index is to be found                       
                         x                                     =                                     'e'                       
           
                         index                                     =                                     findLastIndex(                                     str                                     , x)                       
           
                         if                                     index                                     =                                     =                                     -                                     1                                     :                       
                                                 print                                     (                                     "Character not found"                                     )                       
                         else                                     :                       
                                                 print                                     (                                     'Last index is'                                     , index)                       
           
                         # This code is contributed by shrikant13.                       

C#

                         // C# program to find last index                       
                         // of character x in given string.                       
                         using                                     System;                       
           
                         class                                     GFG {                       
           
                                                 // Returns last index of x if                       
                                                 // it is present Else returns -1.                       
                                                 static                                     int                                     findLastIndex(                                     string                                     str,                                     char                                     x)                       
                                                 {                       
                                                 int                                     index = -1;                       
                                                 for                                     (                                     int                                     i = 0; i < str.Length; i++)                       
                                                 if                                     (str[i] == x)                       
                                                 index = i;                       
                                                 return                                     index;                       
                                                 }                       
                                   
                                                 // Driver code                       
                                                 public                                     static                                     void                                     Main()                       
                                                 {                       
                                                 // String in which char is to be found                       
                                                 string                                     str =                                     "geeksforgeeks"                                     ;                       
                                   
                                                 // char whose index is to be found                       
                                                 char                                     x =                                     'e'                                     ;                       
                                   
                                                 int                                     index = findLastIndex(str, x);                       
                                                 if                                     (index == -1)                       
                                                 Console.WriteLine(                                     "Character not found"                                     );                       
                                                 else                       
                                                 Console.WriteLine(                                     "Last index is "                                     + index);                       
                                                 }                       
                         }                       
           
                         /* This code is contributed by vt_m */                       

PHP

                         <?php                       
                         // PHP program to find last index of                       
                         // character x in given string.                       
           
                         // Returns last index of                       
                         // x if it is present.                       
                         // Else returns -1.                       
                         function                                     findLastIndex(                                     $str                                     ,                                     $x                                     )                       
                         {                       
                                                 $index                                     = -1;                       
                                                 for                                     (                                     $i                                     = 0;                                     $i                                     <                                     strlen                                     (                                     $str                                     );                                     $i                                     ++)                       
                                                 if                                     (                                     $str                                     [                                     $i                                     ] ==                                     $x                                     )                       
                                                 $index                                     =                                     $i                                     ;                       
                                                 return                                     $index                                     ;                       
                         }                       
           
                         // Driver code                       
                         // String in which                       
                         // char is to be found                       
                         $str                                     =                                     "geeksforgeeks"                                     ;                       
           
                         // char whose index                       
                         // is to be found                       
                         $x                                     =                                     'e'                                     ;                       
                         $index                                     = findLastIndex(                                     $str                                     ,                                     $x                                     );                       
                         if                                     (                                     $index                                     == -1)                       
                                                 echo                                     (                                     "Character not found"                                     );                       
                         else                       
                                                 echo                                     (                                     "Last index is "                                     .                                     $index                                     );                       
           
                         // This code is contributed by Ajit.                       
                         ?>                       

Javascript

                         <script>                       
                         // javascript program to find last index                       
                         // of character x in given string.                       
           
                         // Returns last index of x if                       
                         // it is present Else returns -1.                       
                         function                                     findLastIndex(str, x)                       
                         {                       
                                                 let index = -1;                       
                                                 for                                     (let i = 0; i < str.length; i++)                       
                                                 if                                     (str[i] == x)                       
                                                 index = i;                       
                                                 return                                     index;                       
                         }                       
                                   
           
                         // Driver code                       
           
                                                 // String in which char is to be found                       
                                                 let str =                                     "geeksforgeeks"                                     ;                       
                                   
                                                 // char whose index is to be found                       
                                                 let x =                                     'e'                                     ;                       
                                   
                                                 let index = findLastIndex(str, x);                       
                                                 if                                     (index == -1)                       
                                                 document.write(                                     "Character not found"                                     );                       
                                                 else                       
                                                 document.write(                                     "Last index is "                                     + index);                       
                                   
                                                 // This code is contributed by sanjoy_62.                       
                         </script>                       

输出：

Last index is 10

时间复杂度：Θ（n） 方法2（有效：从右侧遍历）： 在上面的方法1中，我们总是遍历完整的字符串。在这种方法中，当存在x时，我们可以避免所有这些情况下的完全遍历。我们的想法是从右边穿过，一找到角色就停下来。

CPP

                         // Simple CPP program to find last index of                       
                         // character x in given string.                       
                         #include <iostream>                       
                         using                                     namespace                                     std;                       
           
                         // Returns last index of x if it is present.                       
                         // Else returns -1.                       
                         int                                     findLastIndex(string& str,                                     char                                     x)                       
                         {                       
                                                 // Traverse from right                       
                                                 for                                     (                                     int                                     i = str.length() - 1; i >= 0; i--)                       
                                                 if                                     (str[i] == x)                       
                                                 return                                     i;                       
           
                                                 return                                     -1;                       
                         }                       
           
                         // Driver code                       
                         int                                     main()                       
                         {                       
                                                 string str =                                     "geeksforgeeks"                                     ;                       
                                                 char                                     x =                                     'e'                                     ;                       
                                                 int                                     index = findLastIndex(str, x);                       
                                                 if                                     (index == -1)                       
                                                 cout <<                                     "Character not found"                                     ;                       
                                                 else                       
                                                 cout <<                                     "Last index is "                                     << index;                       
                                                 return                                     0;                       
                         }                       

JAVA

                         // Java code to find last index                       
                         // character x in given string.                       
                         import                                     java.io.*;                       
                         class                                     GFG {                       
                                   
                         // Returns last index of x if                       
                         // it is present. Else returns -1.                       
                         static                                     int                                     findLastIndex(String str, Character x)                       
                         {                       
                                                 // Traverse from right                       
                                                 for                                     (                                     int                                     i = str.length() -                                     1                                     ; i >=                                     0                                     ; i--)                       
                                                 if                                     (str.charAt(i) == x)                       
                                                 return                                     i;                       
           
                                                 return                                     -                                     1                                     ;                       
                         }                       
                                   
                         // Driver code                       
                         public                                     static                                     void                                     main(String[] args)                       
                         {                       
                                                 String str =                                     "geeksforgeeks"                                     ;                       
                                                 Character x =                                     'e'                                     ;                       
                                                 int                                     index = findLastIndex(str, x);                       
                                                 if                                     (index == -                                     1                                     )                       
                                                 System.out.println(                                     "Character not found"                                     );                       
                                                 else                       
                                                 System.out.println(                                     "Last index is "                                     + index);                       
                         }                       
                         }                       
                         // This code is contributed by Prerna Saini                       

Python3

                         # Simple Python3 program to find last                       
                         # index of character x in given string.                       
           
                         # Returns last index of x if it is                       
                         # present. Else returns -1.                       
                         def                                     findLastIndex(                                     str                                     , x):                       
           
                                                 # Traverse from right                       
                                                 for                                     i                                     in                                     range                                     (                                     len                                     (                                     str                                     )                                     -                                     1                                     ,                                     -                                     1                                     ,                                     -                                     1                                     ):                       
                                                 if                                     (                                     str                                     [i]                                     =                                     =                                     x):                       
                                                 return                                     i                       
           
                                                 return                                     -                                     1                       
           
                         # Driver code                       
                         str                                     =                                     "geeksforgeeks"                       
                         x                                     =                                     'e'                       
                         index                                     =                                     findLastIndex(                                     str                                     , x)                       
           
                         if                                     (index                                     =                                     =                                     -                                     1                                     ):                       
                                                 print                                     (                                     "Character not found"                                     )                       
                         else                                     :                       
                                                 print                                     (                                     "Last index is "                                     ,index)                       
           
                         # This code is contributed by Smitha                       

C#

                         // C# code to find last index                       
                         // character x in given string.                       
                         using                                     System;                       
           
                         class                                     GFG {                       
           
                                                 // Returns last index of x if                       
                                                 // it is present. Else returns -1.                       
                                                 static                                     int                                     findLastIndex(                                     string                                     str,                                     char                                     x)                       
                                                 {                       
                                                 // Traverse from right                       
                                                 for                                     (                                     int                                     i = str.Length - 1; i >= 0; i--)                       
                                                 if                                     (str[i] == x)                       
                                                 return                                     i;                       
                                   
                                                 return                                     -1;                       
                                                 }                       
                                   
                                                 // Driver code                       
                                                 public                                     static                                     void                                     Main()                       
                                                 {                       
                                                 string                                     str =                                     "geeksforgeeks"                                     ;                       
                                                 char                                     x =                                     'e'                                     ;                       
                                                 int                                     index = findLastIndex(str, x);                       
                                                 if                                     (index == -1)                       
                                                 Console.WriteLine(                                     "Character not found"                                     );                       
                                                 else                       
                                                 Console.WriteLine(                                     "Last index is "                                     + index);                       
                                                 }                       
                         }                       
                         // This code is contributed by vt_m                       

PHP

                         <?php                       
                         // Simple PHP program to find last index                       
                         // of character x in given string.                       
           
                         // Returns last index of x if it                       
                         // is present. Else returns -1.                       
                         function                                     findLastIndex(                                     $str                                     ,                                     $x                                     )                       
                         {                       
                                   
                                                 // Traverse from right                       
                                                 for                                     (                                     $i                                     =                                     strlen                                     (                                     $str                                     ) - 1;                                     $i                                     >= 0;                                     $i                                     --)                       
                                                 if                                     (                                     $str                                     [                                     $i                                     ] ==                                     $x                                     )                       
                                                 return                                     $i                                     ;                       
           
                                                 return                                     -1;                       
                         }                       
           
                         // Driver code                       
                         $str                                     =                                     "geeksforgeeks"                                     ;                       
                         $x                                     =                                     'e'                                     ;                       
                         $index                                     = findLastIndex(                                     $str                                     ,                                     $x                                     );                       
                         if                                     (                                     $index                                     == -1)                       
                                                 echo                                     (                                     "Character not found"                                     );                       
                         else                       
                                                 echo                                     (                                     "Last index is "                                     .                                     $index                                     );                       
           
                         // This code is contributed by Ajit.                       
                         ?>                       

Javascript

                         <script>                       
                                                 // Javascript code to find last index character x in given string.                       
                                   
                                                 // Returns last index of x if                       
                                                 // it is present. Else returns -1.                       
                                                 function                                     findLastIndex(str, x)                       
                                                 {                       
                                                 // Traverse from right                       
                                                 for                                     (let i = str.length - 1; i >= 0; i--)                       
                                                 if                                     (str[i] == x)                       
                                                 return                                     i;                       
                                   
                                                 return                                     -1;                       
                                                 }                       
                                   
                                                 let str =                                     "geeksforgeeks"                                     ;                       
                                                 let x =                                     'e'                                     ;                       
                                                 let index = findLastIndex(str, x);                       
                                                 if                                     (index == -1)                       
                                                 document.write(                                     "Character not found"                                     );                       
                                                 else                       
                                                 document.write(                                     "Last index is "                                     + index);                       
                                   
                         </script>                       

输出：

Last index is 10

时间复杂性： O（n）

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