# 958. Check Completeness of a Binary Tree

Given a binary tree, determine if it is a *complete binary tree*.

**Definition of a complete binary tree from** [**Wikipedia**](http://en.wikipedia.org/wiki/Binary_tree#Types_of_binary_trees)**:**\
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:**

![](https://assets.leetcode.com/uploads/2018/12/15/complete-binary-tree-1.png)

```
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:**

![](https://assets.leetcode.com/uploads/2018/12/15/complete-binary-tree-2.png)

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

**Note:**

1. The tree will have between 1 and 100 nodes.

```cpp
// BFS Level Order Traversal
bool isCompleteTree(TreeNode* root) { // time: O(n); space: O(n)
    vector<TreeNode*> nodes({root});
    int i = 0;
    while (i < nodes.size() && nodes[i]) {
        nodes.push_back(nodes[i]->left);
        nodes.push_back(nodes[i]->right);
        ++i;
    }
    while (i < nodes.size() && !nodes[i]) {
        ++i;
    }
    return i == nodes.size();
}
```

```cpp
// BFS Level Order Traversal
bool isCompleteTree(TreeNode* root) { // time: O(n); space: O(n)
    bool end = false;
    queue<TreeNode*> q({root});
    while (!q.empty()) {
        TreeNode* t = q.front(); q.pop();
        if (!t) end = true;
        else {
            if (end) return false;
            q.push(t->left);
            q.push(t->right);
        }
    }
    return true;
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://jimmylin1991.gitbook.io/practice-of-algorithm-problems/tree/958.-check-completeness-of-a-binary-tree.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.