重铸华农荣光 我辈义不容辞

Day 28- interval coverage

#include<iostream>
#include<algorithm>
using namespace std;

const int N=100010;
int n,st,ed;

struct Range{
    int l,r;
    bool operator < (const Range & w) const{
        return l<w.l;
    }
}range[N];

int main()
{
    cin>>st>>ed;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        int l,r;
        cin>>l>>r;
        range[i]={l,r};
    }

    sort(range,range+n);

    int ans=0;
    bool flag=false;
    for(int i=0;i<n;i++)
    {
        int j=i,r=-2e9;
        while(j<n&&range[j].l<=st)
        {
            r=max(r,range[j].r);
            j++;
        }

        if(r<st)
        {
            ans=-1;
            break;
        }

        ans++;

        if(r>=ed)
        {
            flag=true;
            break;
        }

        st=r;
        i=j-1;
    }

    if(flag) cout<<ans;
    else cout<<-1;
}