Leetcode:Path Sum

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.

分析：用DFS解，代码如下：

class Solution {
public:
    bool hasPathSum(TreeNode *root, int sum) {
        return dfs(root, 0, sum);
    }
    
    bool dfs(TreeNode *root, int cur_sum, int sum){
        if(root == NULL) return false;
        cur_sum += root->val;
        
        if(cur_sum == sum && root->left == NULL && root->right == NULL) return true;
        
        return dfs(root->left, cur_sum, sum) || dfs(root->right, cur_sum, sum);
    }
};