958. Check Completeness of a Binary Tree

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958. Check Completeness of a Binary Tree

Description

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:

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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:

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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

Hints/Notes

  • binary tree

Solution

Language: C++

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
 * right(right) {}
 * };
 */
class Solution {
public:
    bool isCompleteTree(TreeNode* root) {
        queue<TreeNode*> q;
        if (root)
            q.push(root);
        bool end = false;
        while (!q.empty()) {
            int n = q.size();
            for (int i = 0; i < n; i++) {
                TreeNode* cur = q.front();
                q.pop();
                if (!cur) {
                    end = true;
                } else {
                    if (end) {
                        return false;
                    }
                    q.push(cur->left);
                    q.push(cur->right);
                }
            }
        }
        return true;
    }
};