区间合并 复习

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

typedef pair<int, int> PII;

void merge(vector<PII>& segs)
{
    vector<PII> res;

    sort(segs.begin(), segs.end());

    // core operations
    int st = -2e9, ed = -2e9;
    for (auto seg : segs)
        if (ed < seg.first)
        {
            if (st != -2e9) res.push_back({st, ed});
            st = seg.first, ed = seg.second;
        }
    else ed = max(ed, seg.second);

    if (st != 2e9) res.push_back({st, ed});

    segs = res;
}

int main()
{
    int n; cin >> n;

    vector<PII> segs;

    for (int i = 1; i <= n; i++)
    {
        int l, r;
        cin >> l >> r;
        segs.push_back({l, r});
    }

    merge(segs);

    cout << segs.size() << endl;

    return 0;
}