以相等的概率生成从1到7的整数-yiteyi-C++库

给定一个函数foo（）以相等的概率返回从1到5的整数，只使用foo（）编写一个函数，以相等的概率返回从1到7的整数。尽量减少对foo（）方法的调用次数。此外，不允许使用任何其他库函数，也不允许使用浮点算法。 解决方案： 我们知道foo（）返回从1到5的整数。我们如何确保1到7之间的整数以相同的概率出现？如果我们以相同的概率从1到7的倍数（比如7，14，21，…）生成整数，我们可以使用模除7，然后加1得到从1到7的概率相等的数字。我们可以使用下面的表达式以相等的概率生成1到21。

null

 5*foo() + foo() -5

让我们看看如何使用上述表达式。 1.对于第一个foo（）的每个值，第二个foo（）的值可以有5种可能的组合。因此，总共有25种可能的组合。 2.上述等式返回的值范围为1到25，每个整数正好出现一次。 3.如果方程的值小于22，则返回模除7，然后加1。否则，再次递归调用该方法。因此，返回每个整数的概率变为1/7。下面的程序显示，表达式只返回1到25之间的每个整数一次。

C++

                         #include <stdio.h>                       
           
                         int                                     main()                       
                         {                       
                                                 int                                     first, second;                       
                                                 for                                     ( first=1; first<=5; ++first )                       
                                                 for                                     ( second=1; second<=5; ++second )                       
                                                 printf                                     (                                     "%d "                                     , 5*first + second - 5);                       
                                                 return                                     0;                       
                         }                       

JAVA

                         // Java code to demonstrate                       
                         // expression returns each integer                       
                         // from 1 to 25 exactly once                       
           
                         class                                     GFG {                       
                                                 public                                     static                                     void                                     main(String[] args)                       
                                                 {                       
                                                 int                                     first, second;                       
                                                 for                                     ( first=                                     1                                     ; first<=                                     5                                     ; ++first )                       
                                                 for                                     ( second=                                     1                                     ; second<=                                     5                                     ; ++second )                       
                                                 System.out.printf (                                     "%d "                                     ,                                     5                                     *first + second -                                     5                                     );                       
                                                 }                       
                         }                       
           
                         // This code is contributed by                       
                         // Smitha Dinesh Semwal                       

Python3

                         # Python3 code to demonstrate                       
                         # expression returns each integer                       
                         # from 1 to 25 exactly once                       
           
                         if                                     name                                     =                                     =                                     '__main__'                                     :                       
                                   
                                                 for                                     first                                     in                                     range                                     (                                     1                                     ,                                     6                                     ):                       
                                                 for                                     second                                     in                                     range                                     (                                     1                                     ,                                     6                                     ):                       
                                                 print                                     (                                     5                                     *                                     first                                     +                                     second                                     -                                     5                                     )                       
           
                         # This code is contributed by Smitha Dinesh Semwal.                       

C#

                         // C# code to demonstrate expression returns                       
                         // each integer from 1 to 25 exactly once                       
                         using                                     System;                       
           
                         class                                     GFG {                       
                                   
                                                 public                                     static                                     void                                     Main()                       
                                                 {                       
                                                 int                                     first, second;                       
           
                                                 for                                     ( first = 1; first <= 5; ++first )                       
                                                 for                                     ( second = 1; second <= 5; ++second )                       
                                                 Console.WriteLine ( 5*first + second - 5);                       
                                                 }                       
                         }                       
           
                         // This code is contributed by Sam007.                       

PHP

                         <?php                       
                         // PHP program to Generate integer                       
                         // from 1 to 7 with equal probability                       
           
                                                 $first                                     ;                       
                                                 $second                                     ;                       
                                                 for                                     (                                     $first                                     = 1;                                     $first                                     <= 5; ++                                     $first                                     )                       
                                                 for                                     (                                     $second                                     = 1;                                     $second                                     <= 5; ++                                     $second                                     )                       
                                                 echo                                     5 *                                     $first                                     +                                     $second                                     - 5,                                     ""                                     ;                       
           
                         // This code is contributed by ajit.                       
                         ?>                       

Javascript

                         <script>                       
           
                         // Javascript Program to demonstrate                       
                         // expression returns each integer                       
                         // from 1 to 25 exactly once                       
           
           
                         // Driver Code                       
           
                                                 let first, second;                       
                                                 for                                     ( first=1; first<=5; ++first )                       
                                                 for                                     ( second=1; second<=5; ++second ) {                       
                                                 document.write( 5*first + second - 5);                       
                                                 document.write(                                     "<br />"                                     );                       
                                                 }                       
           
                         </script>                       

输出：

12..2425

时间复杂性： O（1）

辅助空间： O（1）

下面的程序描述了如何使用foo（）以相同的概率返回1到7。

C++

                         // C++ program to Generate integer from                       
                         // 1 to 5 with equal probability                       
                         #include <stdio.h>                       
           
                         // given method that returns 1 to 5 with equal probability                       
                         int                                     foo()                       
                         {                       
                                                 // some code here                       
                         }                       
           
                         int                                     my_rand()                                     // returns 1 to 7 with equal probability                       
                         {                       
                                                 int                                     i;                       
                                                 i = 5*foo() + foo() - 5;                       
                                                 if                                     (i < 22)                       
                                                 return                                     i%7 + 1;                       
                                                 return                                     my_rand();                       
                         }                       
                         // Driver code                       
                         int                                     main()                       
                         {                       
                                                 printf                                     (                                     "%d "                                     , my_rand());                       
                                                 return                                     0;                       
                         }                       

JAVA

                         // Java program to Generate integer from                       
                         // 1 to 5 with equal probability                       
                         class                                     GfG                       
                         {                       
           
                         // given method that returns 1 to 5 with equal probability                       
                         static                                     int                                     foo()                       
                         {                       
                                                 // some code here                       
                                                 return                                     0                                     ;                       
                         }                       
           
                         // returns 1 to 7 with equal probability                       
                         public                                     static                                     int                                     my_rand()                       
                         {                       
                                                 int                                     i;                       
                                                 i =                                     5                                     *foo() + foo() -                                     5                                     ;                       
                                                 if                                     (i <                                     22                                     )                       
                                                 return                                     i%                                     7                                     +                                     1                                     ;                       
                                                 return                                     my_rand();                       
                         }                       
           
                         // Driver code                       
                         public                                     static                                     void                                     main (String[] args) {                       
           
                                                 System.out.println(my_rand());                       
                         }                       
                         }                       

Python3

                         # Python3 program to Generate integer                       
                         # from 1 to 5 with equal probability                       
                         # given method that returns 1 to 5                       
                         # with equal probability                       
                         def                                     foo():                       
           
                                                 # some code here                       
                                                 return                                     0                                     ;                       
           
                         # returns 1 to 7 with equal probability                       
                         def                                     my_rand():                       
                                                 i                                     =                                     0                                     ;                       
                                                 i                                     =                                     (                                     5                                     *                                     foo())                                     +                                     (foo()                                     -                                     5                                     );                       
                                                 if                                     (i <                                     22                                     ):                       
                                                 if                                     (i <                                     0                                     ):                       
                                                 return                                     (i                                     %                                     7                                     -                                     7                                     )                                     +                                     1                                     ;                       
                                                 else                                     :                       
                                                 return                                     (i                                     %                                     7                                     )                                     +                                     1                                     ;                       
                                   
                                                 return                                     my_rand();                       
           
                         # Driver code                       
                         if                                     __name__                                     =                                     =                                     '__main__'                                     :                       
                                                 print                                     (my_rand());                       
           
                         # This code contributed by PrinciRaj1992                       

C#

                         // C# program to Generate integer from                       
                         // 1 to 5 with equal probability                       
                         using                                     System;                       
                         class                                     GfG                       
                         {                       
                                   
                         // given method that returns 1 to 5 with equal probability                       
                         static                                     int                                     foo()                       
                         {                       
                                                 // some code here                       
                                                 return                                     0;                       
                         }                       
                                   
                         // returns 1 to 7 with equal probability                       
                         public                                     static                                     int                                     my_rand()                       
                         {                       
                                                 int                                     i;                       
                                                 i = 5*foo() + foo() - 5;                       
                                                 if                                     (i < 22)                       
                                                 return                                     i%7 + 1;                       
                                                 return                                     my_rand();                       
                         }                       
                                   
                         // Driver code                       
                         public                                     static                                     void                                     Main () {                       
                                   
                                                 Console.Write(my_rand()+                                     ""                                     );                       
                         }                       
                         }                       

PHP

                         <?php                       
                         // PHP program to Generate integer from                       
                         // 1 to 5 with equal probability                       
                         // given method that returns 1 to 5                       
                         // with equal probability                       
                         function                                     foo()                       
                         {                       
                                                 // some code here                       
                         }                       
           
                         // returns 1 to 7 with equal probability                       
                         function                                     my_rand()                       
                         {                       
                                                 $i                                     ;                       
                                                 $i                                     = 5 * foo() + foo() - 5;                       
                                                 if                                     (                                     $i                                     < 22)                       
                                                 return                                     $i                                     % 7 + 1;                       
                                                 return                                     my_rand();                       
                         }                       
           
                         // Driver code                       
                         echo                                     my_rand();                       
           
                         // This code is contributed by Tushil.                       
                         ?>                       

Javascript

                         <script>                       
           
                         // Javascript program to Generate integer from                       
                         // 1 to 5 with equal probability                       
           
                                                 // given method that returns 1 to 5 with equal probability                       
                                                 function                                     foo()                       
                                                 {                       
                                                 // some code here                       
                                                 return                                     0;                       
                                                 }                       
                                   
                                                 // returns 1 to 7 with equal probability                       
                                                 function                                     my_rand()                       
                                                 {                       
                                                 let i;                       
                                                 i = 5*foo() + foo() - 5;                       
                                                 if                                     (i < 22)                       
                                                 return                                     i%7 + 1;                       
                                                 return                                     my_rand();                       
                                                 }                       
                                   
                                                 // Driver code                       
                                                 document.write(my_rand());                       
                                   
                                                 // This code is contributed by rag2127                       
                                   
                         </script>                       

输出：

-4

时间复杂性： O（1）

辅助空间： O（1）

本文由 阿希什·巴恩瓦尔 并由Geeksforgeks团队审核。如果您发现任何不正确的地方，或者您想分享有关上述主题的更多信息，请写评论

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