NC_15_levelOrder

package org.example.interview.practice;

import com.sun.jmx.remote.internal.ArrayQueue;

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Objects;
import java.util.Queue;

/**
 * @author xianzhe.ma
 * @date 2021/8/21
 */

public class NC_15_levelOrder {

    public static ArrayList<ArrayList<Integer>> levelOrder (TreeNode root) {
        // write code here
        if (Objects.isNull(root)) {
            return new ArrayList<>();
        }
        ArrayList<ArrayList<Integer>> retList = new ArrayList<>();

        Queue<TreeNode> queue = new ArrayDeque<>();
        queue.add(root);
        while (!queue.isEmpty()) {

            ArrayList<TreeNode> levelList = new ArrayList<>();
            ArrayList<Integer> tempList = new ArrayList<>();

            while (!queue.isEmpty()) {

                TreeNode node = queue.poll();
                tempList.add(node.val);
                levelList.add(node);
            }

            for (TreeNode node : levelList) {
                if (Objects.nonNull(node.left)) {
                    queue.add(node.left);
                }
                if (Objects.nonNull(node.right)) {
                    queue.add(node.right);
                }
            }
            levelList = null;
            retList.add(tempList);
        }

        return retList;

    }

    public static class TreeNode {
        int val = 0;
        TreeNode left = null;
        TreeNode right = null;

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

    public static void main(String[] args) {
        TreeNode node0 = new TreeNode(1);
//        TreeNode node1 = new TreeNode(1);
//        TreeNode node2 = new TreeNode(2);
//        node0.right = node1;
//        node0.left = node2;
//        int result = sumNumbers(node0);
//        System.out.println(result);
        levelOrder(node0);
    }
}