Question

我的问题是，作为if / else语句的条件，方法调用到底如何工作？

我知道递归是一种通过更改其参数值来调用自身的方法，可以尝试一种解决方案，如果正确，则停止递归。

这种简单的递归对我来说很有意义：

/* Given a string, compute recursively (no loops) a new string where all the 
 * lowercase 'x' chars have been changed to 'y' chars.
 */
public String changeXY(String str) {
    if(str.length() == 0)
        return str;

    if(str.charAt(0) == 'x')
        return 'y' + changeXY(str.substring(1));

    return str.charAt(0) + changeXY(str.substring(1));
}

但是当将方法调用作为if语句的条件时，我不明白它是如何工作的？正在检查什么？如何确定方法调用是否为true，然后可以返回true以停止递归？如果不是正确的可能性，如何“保存”然后回溯呢？通过返回比较，基本情况如何工作？

/* Given an array of ints, is it possible to choose a group of some of the 
 * ints, such that the group sums to the given target? This is a classic 
 * backtracking recursion problem. Rather than looking at the whole array, 
 * our convention is to consider the part of the array starting at index 
 * start and continuing to the end of the array. The caller can specify the 
 * whole array simply by passing start as 0. No loops are needed -- the 
 * recursive calls progress down the array.
 */
public boolean groupSum(int start, int[] nums, int target) {
    if(start >= nums.length)
        return target == 0;

    if(groupSum(start+1, nums, target - nums[start]))
        return true;

    if(groupSum(start+1, nums, target))
        return true;

    return false;
}

这两个代码均来自此github。

谢谢！

方法调用如何作为条件工作？在Java中进行递归回溯

0 个答案: