LeetCode-112. Path Sum

问题：https://leetcode.com/problems/path-sum/?tab=Description

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. 给定一个二叉树和一个值sum，判断是否存在一个从根节点到叶子节点的路径，使得路径上每个节点值之和等于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.

分析：递归，判断各个路径是否有满足条件、

参考C++代码：

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
bool hasPathSum(TreeNode* root, int sum) {
if(NULL==root) return false;
if(NULL==root->left && NULL==root->right && sum==root->val) return true;
return hasPathSum(root->left,sum-root->val) || hasPathSum(root->right,sum-root->val);
}
};