Path Sum III ---LeetCode

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int pathSum(TreeNode root, int sum) {
if (root == null) return 0;
return helper(root, sum) + pathSum(root.left, sum) + pathSum(root.right, sum);
}
public int helper(TreeNode root, int sum) {
if (root == null) return 0;
int count = 0;
if (root.val == sum) count++;
return count + helper(root.left, sum - root.val) + helper(root.right, sum - root.val);
}
}