poj2376 Cleaning Shifts

思路：

关于区间的贪心。注意特判。

实现：

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

pair<int, int> p[25005];
int n, t;

int main()
{
    cin >> n >> t;
    for (int i = 0; i < n; i++)
    {
        scanf("%d %d", &p[i].first, &p[i].second);
    }
    sort(p, p + n);
    bool flag = true;
    int now_end = 0;
    int cnt = 0;
    for (int i = 0; i < n; i++)
    {
        if (p[i].second <= now_end)
            continue;
        if (p[i].first - now_end > 1)
        {
            flag = false;
            break;
        }
        int j = i, maxn = p[j].second;
        while (j < n && (p[j].first <= now_end || p[j].first - now_end <= 1))
        {
            maxn = max(maxn, p[j].second);
            j++;
        }
        now_end = maxn;
        cnt++;
        if (now_end >= t)
            break;
        i = j - 1;
    }
    if (now_end < t)
    {
        flag = false;
    }
    cout << (flag ? cnt : -1) << endl;
    return 0;
}