Given the root of a binary tree, determine if it is a complete binary tree.

In a complete binary tree, every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.

Example 1:

Input: root = [1,2,3,4,5,6] Output: true Explanation: Every level before the last is full (ie. levels with node-values {1} and {2, 3}), and all nodes in the last level ({4, 5, 6}) are as far left as possible. 

Example 2:

Input: root = [1,2,3,4,5,null,7] Output: false Explanation: The node with value 7 isn't as far left as possible. 

Constraints:

• The number of nodes in the tree is in the range [1, 100].
• 1 <= Node.val <= 1000

给定一个二叉树，确定它是否是一个完全二叉树。

百度百科中对完全二叉树的定义如下：

若设二叉树的深度为 h，除第 h 层外，其它各层 (1～h-1) 的结点数都达到最大个数，第 h 层所有的结点都连续集中在最左边，这就是完全二叉树。（注：第 h 层可能包含 1~ 2h 个节点。）

• 这一题是按层序遍历的变种题。
• 判断每个节点的左孩子是否为空。
• 类似的题目，第 102，107，199 题都是按层序遍历的。

package leetcode import ( "github.com/halfrost/LeetCode-Go/structures" ) // TreeNode definetypeTreeNode= structures.TreeNode/** * Definition for a binary tree node. * type TreeNode struct { * Val int * Left *TreeNode * Right *TreeNode * } */funcisCompleteTree(root*TreeNode) bool { queue, found:= []*TreeNode{root}, falseforlen(queue) >0 { node:=queue[0] //取出每一层的第一个节点queue=queue[1:] ifnode==nil { found=true } else { iffound { returnfalse// 层序遍历中，两个不为空的节点中出现一个 nil } //如果左孩子为nil，则append进去的node.Left为nilqueue=append(queue, node.Left, node.Right) } } returntrue }