Path Sum III ---LeetCode

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https://leetcode.com/problems/path-sum-iii/

这道题与 Path Sum 与 Path Sum II 的区别在于，这道题不需要遍历到叶子节点再结束，同时也不用从根节点开始记录，只要遇到有相加等于 sum 的节点，就记录下来，最终输出有几条这样的路径。

/** * 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);    }}

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