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 2^h nodes inclusive at the last level h.
Example 1
1
/ \
/ \
2 3
/ \ /
4 5 6Input
root = [1,2,3,4,5,6]Output
trueEvery 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
1
/ \
2 3
/ \ \
4 5 7Input
root = [1,2,3,4,5,null,7]Output
falseThe 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