LeetCode 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 binary tree
* 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) {
return dfs(root, 0, sum);
}
private:
bool dfs(TreeNode *root, int cur, int sum) {
if(root == NULL)
return false;
cur += root->val;
//到叶节点时再判断
if(root->left == NULL && root->right == NULL && cur == sum)
return true;
return dfs(root->left, cur, sum) || dfs(root->right, cur, sum);
}
};