void merge(vector<pair<int, int>> &segs)//合并segs中所有有交集的区间
{
    vector<pair<int, int>> res;
    sort(segs.begin(), segs.end());
    int l = -2e9, r = -2e9;
    for (auto seg : segs)
    {
        if (r < seg.first)
        {
            if (l != -2e9)
            {
                res.push_back({l, r});
            }
            l = seg.first, r = seg.second;
        }
        else
        {
            r = max(r, seg.second);
        }
    }
    if (l != -2e9)
    {
        res.push_back({l, r});
    }
    segs = res;
}