958. Check Completeness of a Binary Tree #

Problem Statement #

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: #

package main

// Definition for a binary tree node.
type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func isCompleteTree(root *TreeNode) bool {
	if root == nil {
		return true
	}

	q := []*TreeNode{root}

	for q[0] != nil {
		q = append(q, q[0].Left, q[0].Right)
		q = q[1:]
	}

	for _, node := range q {
		if node != nil {
			return false
		}
	}

	return true
}

... #