递归练习题|集7-yiteyi-C++库

问题1 预测以下程序的输出。下面的fun（）一般做什么？

null

C++

                         #include <iostream>                       
                         using                                     namespace                                     std;                       
           
                         int                                     fun(                                     int                                     n,                                     int                                     * fp)                       
                         {                       
                                                 int                                     t, f;                       
           
                                                 if                                     (n <= 2) {                       
                                                 *fp = 1;                       
                                                 return                                     1;                       
                                                 }                       
                                                 t = fun(n - 1, fp);                       
                                                 f = t + *fp;                       
                                                 *fp = t;                       
                                                 return                                     f;                       
                         }                       
           
                         int                                     main()                       
                         {                       
                                                 int                                     x = 15;                       
                                                 cout << fun(5, &x) << endl;                       
           
                                                 return                                     0;                       
                         }                       

C

                         #include <stdio.h>                       
           
                         int                                     fun (                                     int                                     n,                                     int                                     *fp )                       
                         {                       
                                                 int                                     t, f;                       
           
                                                 if                                     ( n <= 2 )                       
                                                 {                       
                                                 *fp = 1;                       
                                                 return                                     1;                       
                                                 }                       
                                                 t = fun ( n-1, fp );                       
                                                 f = t + *fp;                       
                                                 *fp = t;                       
                                                 return                                     f;                       
                         }                       
           
                         int                                     main()                       
                         {                       
                                                 int                                     x = 15;                       
                                                 printf                                     (                                     "%d"                                     ,fun(5, &x));                       
           
                                                 return                                     0;                       
                         }                       

JAVA

                         import                                     java.io.*;                       
           
                         class                                     GFG {                       
                                                 static                                     int                                     fp =                                     15                                     ;                       
                                                 static                                     int                                     fun (                                     int                                     n)                       
                                                 {                       
                                                 int                                     t, f;                       
                                   
                                                 if                                     ( n <=                                     2                                     )                       
                                                 {                       
                                                 fp =                                     1                                     ;                       
                                                 return                                     1                                     ;                       
                                                 }                       
                                                 t = fun ( n -                                     1                                     );                       
                                                 f = t + fp;                       
                                                 fp = t;                       
                                                 return                                     f;                       
                                                 }                       
                                                 public                                     static                                     void                                     main (String[] args)                       
                                                 {                       
                                                 System.out.println(fun(                                     5                                     ));                       
                                                 }                       
                         }                       
                         // This code is contributed by shubhamsingh10                       

Python3

                         fp                                     =                                     15                       
                         def                                     fun ( n ):                       
                                                 global                                     fp                       
                                                 if                                     ( n <                                     =                                     2                                     ):                       
                                                 fp                                     =                                     1                       
                                                 return                                     1                       
                                   
                                                 t                                     =                                     fun ( n                                     -                                     1                                     )                       
                                                 f                                     =                                     t                                     +                                     fp                       
                                                 fp                                     =                                     t                       
                                                 return                                     f                       
           
                         # Driver code                       
           
                         print                                     (fun(                                     5                                     ))                       
           
                         # This code is contributed by shubhamsingh10                       

C#

                         using                                     System;                       
                                   
                         class                                     GFG{                       
                                                 static                                     int                                     fp = 15;                       
                                                 static                                     int                                     fun (                                     int                                     n)                       
                                                 {                       
                                                 int                                     t, f;                       
                                   
                                                 if                                     ( n <= 2 )                       
                                                 {                       
                                                 fp = 1;                       
                                                 return                                     1;                       
                                                 }                       
                                                 t = fun ( n - 1 );                       
                                                 f = t + fp;                       
                                                 fp = t;                       
                                                 return                                     f;                       
                                                 }                       
                                   
                                                 static                                     public                                     void                                     Main ()                       
                                                 {                       
                                                 Console.Write(fun(5));                       
                                                 }                       
                         }                       
                         // This code is contributed by shubhamsingh10                       

Javascript

                         <script>                       
                         //Javascript Implementation                       
                         var                                     fp = 15;                       
                         function                                     fun( n )                       
                         {                       
                                                 var                                     t, f;                       
                                   
                                                 if                                     ( n <= 2 )                       
                                                 {                       
                                                 fp = 1;                       
                                                 return                                     1;                       
                                                 }                       
                                                 t = fun ( n - 1 );                       
                                                 f = t + fp;                       
                                                 fp = t;                       
                                                 return                                     f;                       
                         }                       
           
                         // Driver Code                       
           
                         document.write(fun(5));                       
           
                         // This code is contributed by shubhamsingh10                       
           
                         </script>                       

输出

该程序计算第n个斐波那契数。语句t=fun（n-1，fp）给出了第（n-1）个斐波那契数，*fp用于存储第（n-2）个斐波那契数。*fp的初始值（在上述程序中为15）无关紧要。下面的递归树显示了从1到10的所有步骤，用于执行fun（5，&x）。

                              (1) fun(5, fp)                              /                                    (2) fun(4, fp)  (10) t = 5, f = 8, *fp = 5                         /                             (3) fun(3, fp)  (9) t = 3, f = 5, *fp = 3                  /                       (4) fun(2, fp)      (8) t = 2, f = 3, *fp = 2          /             (5) fun(1, fp)   (7) t = 1, f = 2, *fp = 1   /(6) *fp = 1

问题2： 预测以下程序的输出。

C++

                         #include <iostream>                       
                         using                                     namespace                                     std;                       
                         void                                     fun(                                     int                                     n)                       
                         {                       
                                                 if                                     (n > 0)                       
                                                 {                       
                                                 fun(n - 1);                       
                                                 cout << n <<                                     " "                                     ;                       
                                                 fun(n - 1);                       
                                                 }                       
                         }                       
           
                         int                                     main()                       
                         {                       
                                                 fun(4);                       
                                                 return                                     0;                       
                         }                       
           
                         // This code is contributed by shubhamsingh10                       

C

                         #include <stdio.h>                       
           
                         void                                     fun(                                     int                                     n)                       
                         {                       
                                                 if                                     (n > 0)                       
                                                 {                       
                                                 fun(n-1);                       
                                                 printf                                     (                                     "%d "                                     , n);                       
                                                 fun(n-1);                       
                                                 }                       
                         }                       
           
                         int                                     main()                       
                         {                       
                                                 fun(4);                       
                                                 return                                     0;                       
                         }                       

JAVA

                         import                                     java.util.*;                       
                                   
                         class                                     GFG{                       
                         static                                     void                                     fun(                                     int                                     n)                       
                         {                       
                                                 if                                     (n >                                     0                                     )                       
                                                 {                       
                                                 fun(n -                                     1                                     );                       
                                                 System.out.print(n+                                     " "                                     );                       
                                                 fun(n -                                     1                                     );                       
                                                 }                       
                         }                       
           
                         public                                     static                                     void                                     main(String[] args)                       
                         {                       
                                                 fun(                                     4                                     );                       
                         }                       
                         }                       
                         // This code is contributed by Shubhamsingh10                       

Python3

                         def                                     fun(n):                       
                                   
                                                 if                                     (n >                                     0                                     ):                       
                                                 fun(n                                     -                                     1                                     )                       
                                                 print                                     (n,end                                     =                                     " "                                     )                       
                                                 fun(n                                     -                                     1                                     )                       
           
                         # driver code                       
           
                         fun(                                     4                                     )                       
           
                         # This code is contributed by shubhamsingh10                       

C#

                         using                                     System;                       
           
                         class                                     GFG{                       
                                                 static                                     void                                     fun(                                     int                                     n)                       
                                                 {                       
                                                 if                                     (n > 0)                       
                                                 {                       
                                                 fun(n - 1);                       
                                                 Console.Write(n+                                     " "                                     );                       
                                                 fun(n - 1);                       
                                                 }                       
                                                 }                       
                                   
                                                 static                                     public                                     void                                     Main ()                       
                                                 {                       
                                                 fun(4);                       
                                                 }                       
                         }                       
           
                         // This code is contributed by shubhamsingh10                       

Javascript

                         <script>                       
                         function                                     fun(n)                       
                         {                       
                                                 if                                     (n > 0)                       
                                                 fun(n - 1);                       
                                                 document.write(n+                                     " "                                     )                       
                                                 fun(n - 1);                       
                         }                       
           
                         // driver code                       
                         fun(4)                       
           
                         // This code is contributed by bobby.                       
                         </script>                       

输出

1 2 1 3 1 2 1 4 1 2 1 3 1 2 1

                     fun(4)                   /                fun(3), print(4), fun(3) [fun(3) prints 1 2 1 3 1 2 1]               /           fun(2), print(3), fun(2) [fun(2) prints 1 2 1]           /       fun(1), print(2), fun(1) [fun(1) prints 1]       /    fun(0), print(1), fun(0) [fun(0) does nothing]

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