POJ 2376

题意：问最少要几个区间才能使区间 [ 1, T ] 全被覆盖掉

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <time.h>
#include <string>
#include <map>
#include <stack>
#include <set>
#include <queue>
#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;
typedef long long ll;
#define PI acos( -1.0 )
const double E = 1e-8;
const int INF = 0x7fffffff;

const int NO = 25000 + 5;
int n, t;
struct ND
{
    int be, en;
}st[NO];

bool cmp( const ND &a, const ND &b )
{
    if( a.be == b.be )
        return a.en > b.en;
    return a.be < b.be;
}

int main()
{
    scanf( "%d%d", &n, &t );
    for( int i = 0; i < n; ++i )
        scanf( "%d%d", &st[i].be, &st[i].en );
    sort( st, st+n, cmp );
    int ans = 0;
    int k = 0;
    for( int i = 0; i < n; ++i )
    {
        if( k+1 >= st[i].be && st[i].en > k )
        {
            ++ans;
            int m = st[i].en, j;
            if( m >= t )
            {
                printf( "%d
", ans );
                return 0;
            }
            for( j = i+1; j < n; ++j )//起始时间在k+1中找最大的终止时间
                if( st[j].be <= k+1 )
                {
                    if( m < st[j].en )
                        m = st[j].en;
                    if( m >= t ) {
                        printf( "%d
", ans );
                        return 0;
                    }
                } else break;
            k = m;
            i = j - 1;
        }
        else if( k+1 < st[i].be )
            break;
    }
    puts( "-1" );
    return 0;
}