LeetCode in Kotlin
958. Check Completeness of a Binary Tree
Medium
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
import com_github_leetcode.TreeNode
import java.util.LinkedList
/*
* Example:
* var ti = TreeNode(5)
* var v = ti.`val`
* Definition for a binary tree node.
* class TreeNode(var `val`: Int) {
* var left: TreeNode? = null
* var right: TreeNode? = null
* }
*/
class Solution {
fun isCompleteTree(root: TreeNode?): Boolean {
if (root == null) {
return true
}
val queue: LinkedList<TreeNode?> = LinkedList<TreeNode?>()
queue.add(root.left)
queue.add(root.right)
var seenNull = false
while (queue.isNotEmpty()) {
val node: TreeNode? = queue.poll()
if (node == null) {
seenNull = true
} else {
if (seenNull) {
return false
}
queue.add(node.left)
queue.add(node.right)
}
}
return true
}
}