POJ 2376 Cleaning Shifts 贪心

//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<sstream>
#include<cmath>
#include<climits>
#include<string>
#include<map>
#include<queue>
#include<vector>
#include<stack>
#include<set>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
#define pb(a) push(a)
#define INF 0x1f1f1f1f
#define lson idx<<1,l,mid
#define rson idx<<1|1,mid+1,r
#define PI  3.1415926535898
template<class T> T min(const T& a,const T& b,const T& c) {
    return min(min(a,b),min(a,c));
}
template<class T> T max(const T& a,const T& b,const T& c) {
    return max(max(a,b),max(a,c));
}
void debug() {
#ifdef ONLINE_JUDGE
#else

    freopen("in.txt","r",stdin);
    //freopen("d:\\out1.txt","w",stdout);
#endif
}
int getch() {
    int ch;
    while((ch=getchar())!=EOF) {
        if(ch!=‘ ‘&&ch!=‘\n‘)return ch;
    }
    return EOF;
}

const int maxn = 25005;
pii da[maxn];
int main()
{
    int n,t;
    while(scanf("%d%d",&n,&t)!=EOF)
    {
        for(int i=0;i<n;i++)
        {
            int l,r; scanf("%d%d",&l,&r);
            da[i]=pii(l,r);
        }
        sort(da,da+n);
        priority_queue<int> q;
        int x=1;
        int cnt=0;
        for(int i=0;i<n;)
        {
            while(i<n&&da[i].first<=x)
                q.push(da[i++].second);
            if(!q.empty())
            {
                int cow=q.top();q.pop();
                if(cow<x)break;
                x=cow+1;
                cnt++;
                if(x>t)break;
            }else break;
        }
        printf("%d\n",x<=t?-1:cnt);
    }
    return 0;
}