剑指60.把二叉树打印成多行

题目描述

从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。

 

 

思路

 

见 二叉树层序遍历问题总结

 

 

解法

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

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

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

    }
}
*/
public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer> > ans = new ArrayList<>();
        if (pRoot == null) return ans;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(pRoot);
        while (!queue.isEmpty()){
            int levelNums = queue.size();
            ArrayList<Integer> list = new ArrayList<>();
            for (int i = 0; i < levelNums; i++) {
                TreeNode cur = queue.poll();
                list.add(cur.val);
                if (cur.left != null) queue.offer(cur.left);
                if (cur.right != null) queue.offer(cur.right);
            }
            ans.add(list);
        }
        return ans;
    }
}