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
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public boolean isCompleteTree(TreeNode root) {
Queue<TreeNode> bfs = new LinkedList<TreeNode>();
bfs.offer(root);
while(bfs.peek()!=null){
TreeNode node = bfs.poll();
bfs.offer(node.left);
bfs.offer(node.right);
}
while (!bfs.isEmpty() && bfs.peek() == null){
bfs.poll();
}
return bfs.isEmpty();
}
}