Set Intersection

• Time : $O(nlogn)$
• Space : $O(1)$

int Solution::setIntersection(vector<vector<int>> &A) {
    sort(begin(A), end(A), [](auto& a, auto& b) {
        if(a[1] != b[1]) return a[1] < b[1];
        return a[0] > b[0];
    });
    int res = 2, mi = A[0][1] - 1, ma = A[0][1];
    for(int i = 1; i < A.size(); i++) {
        int l = A[i][0], r = A[i][1];
        if(ma < l) {
            res += 2;
            ma = r, mi = r - 1;
        } else if(ma == l) {
            res += 1;
            mi = ma, ma = r;
        } else if(mi < l) {
            res += 1;
            if(ma == r) mi = ma - 1;
            else mi = ma, ma = r;
        }
    }
    return res;
}