Given a binary tree, determine if it is a complete binary tree.
Definition of a complete binary tree from Wikipedia:
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: [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: [1,2,3,4,5,null,7]
Output: false
Explanation: The node with value 7 isn't as far left as possible.
Note:
- The tree will have between 1 and 100 nodes.
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。）
示例 1：
输入：[1,2,3,4,5,6]
输出：true
解释：最后一层前的每一层都是满的（即，结点值为 {1} 和 {2,3} 的两层），且最后一层中的所有结点（{4,5,6}）都尽可能地向左。
示例 2：
输入：[1,2,3,4,5,null,7] 输出：false 解释：值为 7 的结点没有尽可能靠向左侧。
提示：
- 树中将会有 1 到 100 个结点。
36 ms
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * public var val: Int 5 * public var left: TreeNode? 6 * public var right: TreeNode? 7 * public init(_ val: Int) { 8 * self.val = val 9 * self.left = nil 10 * self.right = nil 11 * } 12 * } 13 */ 14 class Solution { 15 func isCompleteTree(_ root: TreeNode?) -> Bool { 16 var root = root 17 var queue:[TreeNode?] = [TreeNode?]() 18 var leaf:Bool = false 19 queue.append(root) 20 21 while(!queue.isEmpty) 22 { 23 root = queue.removeFirst() 24 if (leaf && (root?.left != nil || root?.right != nil)) || (root?.left == nil && root?.right != nil) 25 { 26 return false 27 } 28 if root?.left != nil 29 { 30 queue.append(root?.left) 31 } 32 if root?.right != nil 33 { 34 queue.append(root?.right) 35 } 36 else 37 { 38 leaf = true 39 } 40 } 41 return true 42 } 43 }