## DEV Community

Abhishek Chaudhary

Posted on

# 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`

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, 0)]
keys = {}
while len(nodes) > 0:
curr, l = nodes.pop()
keys[l] = curr.val
if curr.left:
nodes.append((curr.left, 2 * l + 1))
if curr.right:
nodes.append((curr.right, 2 * l + 2))
mkey = max(keys.keys())
for l in range(mkey):
if l not in keys:
return False
return True
``````