二叉树中和为某一个值的路径

输入一棵二叉树和一个整数，打印出二叉树中节点值的和为输入整数的所有路径。从树的根节点开始往下一直到叶节点所经过的节点形成一条路径。

来源：https://leetcode-cn.com/problems/er-cha-shu-zhong-he-wei-mou-yi-zhi-de-lu-jing-lcof

学习一下遍历二叉树从根节点到叶子节点路径的问题，虽然效率不高，但是毕竟是自己写的，思路清晰，特此记录！

import java.util.ArrayList;
import java.util.List;

class Solution {

    public static void main(String[] args) {
        TreeNode root = new TreeNode(5);
        root.left = new TreeNode(4);
        root.right = new TreeNode(8);
        root.left.left = new TreeNode(11);
        root.left.left.left = new TreeNode(7);
        root.left.left.right = new TreeNode(2);
        root.right.left = new TreeNode(13);
        root.right.right = new TreeNode(4);
        root.right.right.left = new TreeNode(5);
        root.right.right.right = new TreeNode(1);
        List<List<Integer>> lists = new Solution().pathSum(root, 22);
        System.out.println(lists);
    }


    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> lists = new ArrayList<>();
        if (root==null) return lists;
        ArrayList<Integer>  local = new ArrayList<>();
        help(lists,local,root,sum);
        return lists;
    }

    private void help(List<List<Integer>> lists, ArrayList<Integer> local, TreeNode node, int sum) {
        local.add(node.val);
        if (node.left ==null && node.right == null){
            ArrayList<Integer> oldlocal = new ArrayList<>(local);
            int Sum = 0;
            Sum  = local.stream().reduce(Sum, (a, b) -> a + b);
            if (Sum == sum){
                lists.add(oldlocal);
            }
        }
        if (node.left!=null) {
            help(lists, local, node.left, sum);
            local.remove(local.size() - 1);
        }
        if (node.right!=null) {
            help(lists, local, node.right, sum);
            local.remove(local.size() - 1);
        }

    }
}