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# 0958. Check Completeness of a Binary Tree

<https://leetcode.com/problems/check-completeness-of-a-binary-tree>

## Description

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`

## ac

```java
```