区间合并

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
typedef pair<int,int>PII;
const int N=100010;
int n;
vector<PII>segs;
void merge(vector<PII>&segs){
    vector<PII>res;
    sort(segs.begin(),segs.end());
    int st=-2e9,ed=-2e9;
    for(auto item:segs){
        if(ed<item.first){
            if(st!=-2e9)res.push_back({st,ed});
            st=item.first,ed=item.second;
        }
        else ed=max(ed,item.second);
    }
    if(st!=-2e9)res.push_back({st,ed});
    segs=res;
}
int main()
{
    cin>>n;
    for(int i=0;i<n;i++){
        int x,y;
        cin>>x>>y;
        segs.push_back({x,y});
    }

    merge(segs);
    cout<<segs.size()<<endl;
    return 0;
}