算法:从上往下打印二叉树

从上往下打印二叉树

从上往下打印二叉树

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。

分析

简单的二叉树的BFS

代码

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

public class Solution {
    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
        ArrayList<Integer> res = new ArrayList<>(256);
        if (root == null) return res;

        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode cur = queue.poll();
                res.add(cur.val);
                if (cur.left != null) queue.offer(cur.left);
                if (cur.right != null) queue.offer(cur.right);
            }
        }
        return res;
    }
}