C 中的尾递归

发布于 2024-09-27 15:29:20 字数 297 浏览 3 评论 0原文

我试图编写递归函数来查找数字的阶乘。

    int factorial(int input,int *answer)
    {
       if ( input ==0 )        
       {                       
        return 0;
       }

       *answer  = *answer * input;
       factorial(input -1, answer);
    }

对于这个功能你有什么想说的吗？是尾递归吗？

原文

I was trying to write recursion function,to find factorial of a number.

    int factorial(int input,int *answer)
    {
       if ( input ==0 )        
       {                       
        return 0;
       }

       *answer  = *answer * input;
       factorial(input -1, answer);
    }

What will you say about this function? Is it tail recursive?

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箜明 2024-10-04 15:29:20

在执行尾递归函数（尤其是尾递归函数）时，除了另一个具有更友好界面的函数之外，拥有一个辅助函数通常会很有帮助。友好的接口函数实际上只是设置不太友好的函数的参数。

static unsigned factorial_helper(unsigned input, unsigned acc) {
       if (intput == 0) {
           return acc;
       }
       return factorial_helper(input-1, acc * input);
}

unsigned factorial(int input) {
    if (input < 0) {
        do_something_bad();
    }
    return factorial_helper(input, 1);
}

通过传递累加器值，您可以避免使用指针或在从被调用函数返回时进行任何计算，这使得函数真正成为尾递归。

When doing tail recursive functions (especially tail recursive functions) it is often helpful to have a helper function in addition to another function which has a more friendly interface. The friendly interface function really just sets up the less friendly function's arguments.

static unsigned factorial_helper(unsigned input, unsigned acc) {
       if (intput == 0) {
           return acc;
       }
       return factorial_helper(input-1, acc * input);
}

unsigned factorial(int input) {
    if (input < 0) {
        do_something_bad();
    }
    return factorial_helper(input, 1);
}

By passing an accumulator value you avoid having to use pointers or do any computations upon returning from called functions, which makes the functions truely tail recursive.

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