head & 的区别尾递归

问题描述

我正在尝试找出这两种递归策略之间的区别.

I'm trying to get the difference between these 2 recursive strategies.

我被告知的定义如下:

尾递归:如果调用返回后无需执行任何操作，即调用返回时，调用函数立即返回返回值，则调用是尾递归的

Tail Recursion: A call is tail-recursive if nothing has to be done after the call returns i.e. when the call returns, the returned value is immediately returned from the calling function

头递归:当函数的第一条语句是递归调用时，调用就是头递归.

Head Recursion: A call is head-recursive when the first statement of the function is the recursive call.

推荐答案

在 head recursion 中，递归调用，当它发生时，在函数中的其他处理之前(想想它发生在函数的顶部或头部).

In head recursion, the recursive call, when it happens, comes before other processing in the function (think of it happening at the top, or head, of the function).

在尾递归中，情况正好相反——处理发生在递归调用之前.在这两种递归风格之间进行选择似乎是随意的，但选择可以产生很大的不同.

In tail recursion, it’s the opposite—the processing occurs before the recursive call. Choosing between the two recursive styles may seem arbitrary, but the choice can make all the difference.

在路径开头有一个单一递归调用的路径的函数使用所谓的头递归.先前展示的阶乘函数使用头部递归.一旦确定需要递归，它所做的第一件事就是用递减的参数调用自己.在路径末尾具有单个递归调用的函数使用尾递归.参考这篇文章

A function with a path with a single recursive call at the beginning of the path uses what is called head recursion. The factorial function of a previous exhibit uses head recursion. The first thing it does once it determines that recursion is needed is to call itself with the decremented parameter.A function with a single recursive call at the end of a path is using tail recursion.Refer this article

示例递归:

public void tail(int n)         |     public void head(int n)
{                               |     {
    if(n == 1)                  |         if(n == 0)
        return;                 |             return;
    else                        |         else
        System.out.println(n);  |             head(n-1);
                                |
    tail(n-1);                  |         System.out.println(n);
}                               |     }

如果递归调用发生在方法的末尾，则称为尾递归.尾递归类似于循环.方法在跳转到下一个递归调用之前执行所有语句.

If the recursive call occurs at the end of a method, it is called a tail recursion. The tail recursion is similar to a loop. The method executes all the statements before jumping into the next recursive call.

如果递归调用发生在方法的开头，则称为头递归.方法在跳转到下一个递归调用之前保存状态.

If the recursive call occurs at the beginning of a method, it is called a head recursion. The method saves the state before jumping into the next recursive call.

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