LeetCode -- Path Sum III分析及实现方法

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); } }

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