题目描述
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。
解题
import java.util.ArrayList;
import java.util.Queue;
import java.util.LinkedList;
/**
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
*/
public class Solution {
public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
ArrayList<Integer> list = new ArrayList<>();
if(root==null)
return list;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
//队列一直不为空的时候执行
while (!queue.isEmpty()){
//取出来队列先入队列的顶的元素
list.add(queue.peek().val);
//取出队列顶元素
TreeNode poll = queue.poll();
//
if(poll.left!=null)
queue.offer(poll.left);
if(poll.right!=null)
queue.offer(poll.right);
}
return list;
}
}