poj2376 Cleaning Shifts

思路：
关于区间的贪心。注意特判。
实现：
 1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 using namespace std;
 5 
 6 pair<int, int> p[25005];
 7 int n, t;
 8 
 9 int main()
10 {
11     cin >> n >> t;
12     for (int i = 0; i < n; i++)
13     {
14         scanf("%d %d", &p[i].first, &p[i].second);
15     }
16     sort(p, p + n);
17     bool flag = true;
18     int now_end = 0;
19     int cnt = 0;
20     for (int i = 0; i < n; i++)
21     {
22         if (p[i].second <= now_end)
23             continue;
24         if (p[i].first - now_end > 1)
25         {
26             flag = false;
27             break;
28         }
29         int j = i, maxn = p[j].second;
30         while (j < n && (p[j].first <= now_end || p[j].first - now_end <= 1))
31         {
32             maxn = max(maxn, p[j].second);
33             j++;
34         }
35         now_end = maxn;
36         cnt++;
37         if (now_end >= t)
38             break;
39         i = j - 1;
40     }
41     if (now_end < t)
42     {
43         flag = false;
44     }
45     cout << (flag ? cnt : -1) << endl;
46     return 0;
47 }