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.

              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.

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     public int val;
 5  *     public TreeNode left;
 6  *     public TreeNode right;
 7  *     public TreeNode(int x) { val = x; }
 
 8  * }
 9  */
10 public class Solution {
11     public bool HasPathSum(TreeNode root, int sum) {
12         return DFS(root, 0, sum);
13     }
14     
15     private bool DFS(TreeNode node, int cur, int sum)
16     {
17         if (node == null) return false;
18             
19         if (node.left == null
 
 && node.right == null)
20         {
21             return cur + node.val == sum;
22         }
23         
24         return DFS(node.left, cur + node.val, sum) || DFS(node.right, cur + node.val, sum);
25     }
26 }

Leetcode 112: Path Sum