java循环

import java.util.ArrayList;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
import java.util.*;
public class Solution {
    public int sum(List<Integer> list) {
        return list.stream().reduce(0, (s1, s2) -> s1 + s2);
    }
    public ArrayList<ArrayList<Integer>> FindPath(TreeNode root,int target) {
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
        if (root == null) {
            return list;
        }
        Stack<TreeNode> queue = new Stack<>();
        Stack<ArrayList<Integer>> paths = new Stack<>();
        queue.push(root);
        ArrayList<Integer> vals = new ArrayList<>();
        vals.add(root.val);
        paths.push(vals);
        while (!queue.isEmpty()) {
            TreeNode node = queue.pop();
            ArrayList<Integer> path = paths.pop();
            if (node.left == null && node.right == null && sum(path) == target) {
                list.add(path);
            }
            if (node.right != null) {
                queue.push(node.right);
                ArrayList<Integer> integers = new ArrayList<>(path);
                integers.add(node.right.val);
                paths.add(integers);
            }
            if (node.left != null) {
                queue.push(node.left);
                ArrayList<Integer> integers = new ArrayList<>(path);
                integers.add(node.left.val);
                paths.push(integers);
            }
        }
        return list;

    }
}