Meeting rooms

• Time : $O(nlogn)$
• Space : $O(n)$

int Solution::solve(vector<vector<int> > &A) {
    sort(begin(A), end(A));
    priority_queue<int, vector<int>, greater<int>> q;
    int l = 0, r = 0, n = A.size(), res = 0;
    while(r < n) {
        int s = A[l][0], e = A[r][0];
        while(q.size() and q.top() <= s) q.pop();
        while(r < n and A[r][0] == s) q.push(A[r++][1]);
        res = max(res, (int)q.size());
        l = r;
    }
    return res;
}