Leetcode 113. Path Sum II

题目链接

https://leetcode.com/problems/path-sum-ii/description/

题目描述

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

      5
     / \
    4   8
   /   / \
  11  13  4
 /  \    / \
7    2  5   1

Return:

[
   [5,4,11,2],
   [5,8,4,5]
]

题解

递归遍历每一个节点，计算节点的总和,但满足条件的时候就把路径添加到List中。

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> list = new ArrayList<>();
        findHelper(root, list, new ArrayList<Integer>(), sum);
        return list;
    }
    public void findHelper(TreeNode root, List<List<Integer>> list, List<Integer> tempList,int sum) {
        if (root == null) { return ; }
        tempList.add(root.val);
        if (root.left == null && root.right == null && sum == root.val) {
            list.add(new ArrayList<>(tempList));
        }
        findHelper(root.left, list, tempList, sum - root.val);
        findHelper(root.right, list, tempList, sum - root.val);
        tempList.remove(tempList.size() - 1);
    }
}