poj2376

排序+贪心

View Code

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;

#define maxn 25005

struct Interval
{
    int s, e;
}interval[maxn];

int n, t;

bool operator < (const Interval &a, const Interval &b)
{
    if (a.s != b.s)
        return a.s < b.s;
    return a.e < b.e;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    scanf("%d%d", &n, &t);
    for (int i = 0; i < n; i++)
        scanf("%d%d", &interval[i].s, &interval[i].e);
    sort(interval, interval + n);
    int temp = 0;
    int ans = 0;
    int i = 0;
    while (temp < t && i < n)
    {
        ans++;
        int top = temp;
        if (interval[i].s > temp + 1)
        {
            printf("-1\n");
            return 0;
        }
        while (i < n && interval[i].s <= temp + 1)
        {
            top = max(top, interval[i].e);
            i++;
        }
        temp = top;
    }
    if (temp < t)
        printf("-1\n");
    else
        printf("%d\n", ans);
    return 0;
}