LeetCode -- Path Sum III

题目描述：
You are given a binary tree in which each node contains an integer value.


Find the number of paths that sum to a given value.


The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).


The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.


给定一个二叉树，遍历过程中收集所有可能路径的和，找出和等于X的路径树。


思路：
设当前节点为root,分别收集左右节点路径和的集合，merge到当前集合中；
将当前节点添加到数组中，构成新的可能路径。


实现代码：

/** * 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);    }}