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.

C++版

class Solution {

public:

    bool hasPathSum(TreeNode *root, int sum) {

        if (root == NULL) return false;  

        if (root->left == NULL && root->right == NULL && sum - root->val == 0) return true;  

        return hasPathSum(root->left, sum - root->val) || hasPathSum(root->right, sum - root->val);          

    }   

};

Java版本：

/**

 * Definition for binary tree

 * public class TreeNode {

 *     int val;

 *     TreeNode left;

 *     TreeNode right;

 *     TreeNode(int x) { val = x; }

 * }

 */

public class Solution {

    public boolean hasPathSum(TreeNode root, int sum) {  

        if (root == null) return false;  

        if (root.left == null && root.right == null && sum - root.val == 0) return true;  

        return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);          

    }  

}