# ---
# title: 958. Check Completeness of a Binary Tree
# id: problem958
# author: Tian Jun
# date: 2020-10-31
# difficulty: Medium
# categories: Tree
# link: <https://leetcode.com/problems/check-completeness-of-a-binary-tree/description/>
# hidden: true
# ---
# 
# Given the `root` of a binary tree, determine if it is a _complete binary
# tree_.
# 
# In a **[complete binary
# tree](http://en.wikipedia.org/wiki/Binary_tree#Types_of_binary_trees)** ,
# 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:**
# 
# ![](https://assets.leetcode.com/uploads/2018/12/15/complete-binary-tree-1.png)
# 
#     
#     
#     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:**
# 
# ![](https://assets.leetcode.com/uploads/2018/12/15/complete-binary-tree-2.png)
# 
#     
#     
#     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`
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
