题解 | #判断是不是完全二叉树#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return bool布尔型
     */
    public boolean isCompleteTree (TreeNode root) {
        // write code here
        if(root == null){
            return true;
        }
        Deque<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        boolean nullNode = false;
        while(!queue.isEmpty()){
            root = queue.poll();
            if(root==null){
                nullNode = true;
            }else{
                if(nullNode){
                    return false;
                }
                queue.offer(root.left);
                queue.offer(root.right);
            }
        }
        return true;
        
    }
}