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.

/**
 * 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) {
        if(!root) return false;
        if(!root->left && !root->right) return sum == root->val;
        return hasPathSum(root->left, sum-root->val) || 
            hasPathSum(root->right, sum-root->val);
    }
};