C和指针之函数之实现阶乘和斐波那契数(递归和非递归)

   

    

     

      

     
     

      

       #include <stdio.h>
      
     
    

     

      

     
     

      
 
      
     
    

     

      

     
     

      

       int num = 0;
      
     
    

     

      

     
     

      

       //递归实现斐波那契数
      
     
    

     

      

     
     

      

       // n <=2, f(n) = 1, n > 2 f(n) = f(n - 1) + f();
      
     
    

     

      

     
     

      

       long fibonacci(int n)
      
     
    

     

      

     
     

      

       {
      
     
    

     

      

     
     

      

        //计算fibonacci(3)计算了多少次
      
     
    

     

      

     
     

      

        if (n == 3)
      
     
    

     

      

     
     

      

        num++;
      
     
    

     

      

     
     

      

        if (n <= 2)
      
     
    

     

      

     
     

      

        {
      
     
    

     

      

     
     

      

        printf("num is %d\n", num);
      
     
    

     

      

     
     

      

        return 1;
      
     
    

     

      

     
     

      

        }
      
     
    

     

      

     
     

      

        return fibonacci(n - 1) + fibonacci(n - 2);
      
     
    

     

      

     
     

      

       }
      
     
    

     

      

     
     

      

       
      
     
    

     

      

     
     

      

       
      
     
    

     

      

     
     

      

       //非递归实现斐波那契数
      
     
    

     

      

     
     

      

       long fibonacci1(int n)
      
     
    

     

      

     
     

      

       {
      
     
    

     

      

     
     

      

        long result = 1, pre_result = 1, next_pre_result;
      
     
    

     

      

     
     

      

        while (n > 2)
      
     
    

     

      

     
     

      

        {
      
     
    

     

      

     
     

      

        n -= 1;
      
     
    

     

      

     
     

      

        next_pre_result = pre_result;
      
     
    

     

      

     
     

      

        pre_result = result;
      
     
    

     

      

     
     

      

        result = pre_result + next_pre_result;
      
     
    

     

      

     
     

      

        }
      
     
    

     

      

     
     

      

        return result;
      
     
    

     

      

     
     

      

       }
      
     
    

     

      

     
     

      
 
      
     
    

     

      

     
     

      
 
      
     
    

     

      

     
     

      

       //递归实现n的阶乘
      
     
    

     

      

     
     

      

       //n <= 1, f(n) = 1, n > 1 f(n) = n * f(n - 1);
      
     
    

     

      

     
     

      

       long factorial(int n)
      
     
    

     

      

     
     

      

       {
      
     
    

     

      

     
     

      

        if (n == 1)
      
     
    

     

      

     
     

      

        return 1;
      
     
    

     

      

     
     

      

        return n * factorial(n - 1);
      
     
    

     

      

     
     

      

       }