662. Maximum Width of Binary Tree

https://leetcode.com/problems/maximum-width-of-binary-tree/description/

/**
 * 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:
    int widthOfBinaryTree(TreeNode* root) {
        int left = 0, right = 0, res = 0;
        queue<pair<int,TreeNode*>> q;
        if (root != NULL)   q.push({1, root});
        while (!q.empty()) {
            int qsz = q.size();
            for (int i = 0; i < qsz; i++) {
                int idx = q.front().first;
                TreeNode* cur = q.front().second;
                q.pop();
                
                if (i == 0)     left = idx;
                if (i == qsz - 1)   right = idx;
                if (cur->left)  q.push( { idx *2, cur->left });
                if (cur->right) q.push( { idx *2 + 1, cur->right });
            }
            res = max(res, right-left+1);
        }
        return res;
    }
};