Check Completeness of a Binary Tree.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isCompleteTree(TreeNode* root) {
        if(!root)return true;
        vector<pair<TreeNode*, int>> nodes;
        nodes.emplace_back(root, 0);
        int i = 0;
        while(i < nodes.size())
        {
            auto node = nodes[i].first;
            int label = nodes[i].second;
            if(node->left)nodes.emplace_back(node->left, 2 * label + 1);
            if(node->right)nodes.emplace_back(node->right, 2 * label + 2);
            ++i;
        }
        return nodes.back().second + 1 == nodes.size();
    }
};