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;
        }

        Queue<TreeNode> queue = new LinkedList<>();

        queue.offer(root);
        boolean shouldEnd = false;
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            if (node == null) {
                shouldEnd = true;
                continue;
            }
            if (shouldEnd) {
                return false;
            }
            queue.offer(node.left);
            queue.offer(node.right);
        }

        return true; 
    }
}