README.md

958. Check Completeness of a Binary Tree

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

Solutions (Python)

1. Solution

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isCompleteTree(self, root: Optional[TreeNode]) -> bool:
        nodes = [root]
        depth = 0

        while True:
            children = []

            if nodes[0] == None:
                return True

            if len(nodes) != 2 ** depth:
                return False

            for node in nodes:
                if node is not None:
                    children.append(node.left)
                    children.append(node.right)

            for i in range(1, len(children)):
                if children[i - 1] is None and children[i] is not None:
                    return False

            nodes = children
            depth += 1