POJ 2376

#include<iostream>//by chengdacaizi.
#include<stdio.h>
#define MAXN 25005
using namespace std;

struct Cows 
{
    int begin;
    int end;
};

Cows cow[MAXN];

int compare(const void * i,const void * j);
int main()
{
    //freopen("acm.acm","r",stdin);
    int i;
    int j;
    int n;
    int t;
    bool boo;
    int last;
    int max;
    int tem;
    int max_num;
    int result;
    scanf("%d %d",&n,&t);
    for(i = 0; i < n; ++ i)
    {
        scanf("%d %d",&cow[i].begin,&cow[i].end);
    }
    qsort(cow,n,sizeof(Cows),compare);
    last = 1;
    i = 0;
    max = 0;
    result = 0;
    boo = true;
    while(1)
    {
        max = -1;
        while(cow[i].begin <= last)
        {
            if((tem = cow[i].end - last) > max)
            {
                max = tem;
                max_num = i;
            }
            ++ i;
        }
        if(max == -1)
        {
        //    cout<<cow[i].begin<<"   000000000000"<<endl;//很巧合的处理，当数组越界的时候，当然，还没有完成，那么自动跳出，cout<<-1；
            boo = false;
            break;
        }
        ++ result;
        if(cow[max_num].end >= t)
        {
            break;
        }
        else
        {
            last = cow[max_num].end + 1;
        }
    }
    if(boo)
        cout<<result<<endl;
    else
        cout<<-1<<endl;

}

int compare(const void * i,const void * j)
{
    return *((int *)i) - *((int *)j);
}