BZOJ 3389--Cleaning Shifts安排值班(贪心)

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<iostream>
using namespace std;
int N,T;
struct cow{
    int l,r;
}c[30000];
bool cmp(cow p,cow q){
    if(p.l==q.l) return p.r<q.r;
    return p.l<q.l;
}
int main(){
    int ans=0;
    scanf("%d%d",&N,&T);
    for(int i=1;i<=N;i++)
        scanf("%d%d",&c[i].l,&c[i].r);
    sort(c+1,c+1+N,cmp);
    int t=0,k=1;
    while(t<T&&k<=N){
        int s=t;
        while(c[k].l<=(t+1)&&k<=N){
            if(c[k].r>s) s=c[k].r;
            k++;
        }
        if(t==s) break;
        t=s;
        ans++;
    }
    if(t<T) ans=-1;
    printf("%d\n",ans);
    return 0;
}