Print the binary tree from top to bottom
Question:
Print each node of the binary tree from top to bottom, and print the nodes at the same level from left to right.
Code:
package com.sjsq.test;
import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
/**
* @author shuijianshiqing
* @date 2020/5/24 10:43
*/
/**
* 从上往下打印出二叉树的每个节点,同层节点从左至右打印。
*/
public class Solution {
public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
// 定义双向队列
Deque<TreeNode> deque = new LinkedList<>();
// 定义数组来存放结果
ArrayList<Integer> result = new ArrayList<>();
if(root == null){
return result;
}
deque.add(root);
while(!deque.isEmpty()){
TreeNode node = deque.getFirst();
deque.pollFirst();
result.add(node.val);
// 判断有没有左子树
if(node.left != null){
deque.addLast(node.left);
}
// 判断有没有右子树
if(node.right != null){
deque.addLast(node.right);
}
}
return result;
}
}