Leetcode：112. Path Sum （求Tree中是否存在路径的和等于给定值）

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:

Given the below binary tree and sum = 22,

5

/ \

4 8

/ / \

11 13 4

/ \ \

7 2 1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

代码：

public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) { val = x; }
}

class Solution {
/**
***采用递归的方法，我们用递归来实现！！！
*非常的简单 ：
*其基本思想是从总和中减去当前节点的值，
*直到它到达一个叶节点，结果等于0，那么我们知道我们得到了一个命中。
*否则，最后的结果不能为0。**
*/
public boolean hasPathSum(TreeNode root, int sum) {
if(root == null) return false;
if(root.left == null && root.right == null && sum - root.val == 0) return true;
return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
}
}