從上往下打印二叉樹

題目鏈接:https://www.nowcoder.com/practice/7fe2212963db4790b57431d9ed259701?tpId=13&tqId=11175&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking

 

二叉樹的層次遍歷

import java.util.*;
public class Solution {
    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        ArrayList<Integer> list = new ArrayList<Integer>();
        
        queue.add(root);
        
        while(!queue.isEmpty()){
            TreeNode node = queue.remove();
            if(node == null){
                continue;
            }
            list.add(node.val);
            queue.add(node.left);
            queue.add(node.right);
        }
        return list;
    }
}