/** * Definition for a binary tree node. * public class TreeNode { *     public int val; *     public TreeNode left; *     public TreeNode right; *     public TreeNode(int x) { val = x; } * } */public class Solution {        PRivate int _sum;    private int _count;    public int PathSum(TreeNode root, int sum)     {		_count = 0;		_sum = sum;    	Travel(root, new List<int>());    	return _count;    }        private void Travel(TreeNode current, List<int> ret){		if(current == null){			return ;		}				if(current.val == _sum){			_count ++;		}				var left = new List<int>();		Travel(current.left, left);				var right = new List<int>();		Travel(current.right, right);				ret.AddRange(left);		ret.AddRange(right);				for(var i = 0;i < ret.Count; i++){			ret[i] += current.val;			if(ret[i] == _sum){				_count ++;			}		}		ret.Add(current.val);				//Console.WriteLine(ret);    }}