[leetcode][tree][dfs] Path Sum

题目：

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.

/** * 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) return root->val == sum ? true : false;//叶节点        int sumNew = sum - root->val;        if(hasPathSum(root->left, sumNew)) return true;        return hasPathSum(root->right, sumNew);    }};