POJ 2376 Cleaning Shifts

 1 #include <iostream>
 2 #include <algorithm>
 3 #include <map>
 4 #include <vector>
 5 #include <functional>
 6 #include <string>
 7 #include <cstring>
 8 #include <queue>
 9 #include <set>
10 #include <cmath>
11 #include <cstdio>
12 using namespace std;
13 #define IOS ios_base::sync_with_stdio(false)
14 #define TIE std::cin.tie(0)
15 #define MIN2(a,b) (a<b?a:b)
16 #define MIN3(a,b) (a<b?(a<c?a:c):(b<c?b:c))
17 #define MAX2(a,b) (a>b?a:b)
18 #define MAX3(a,b,c)  (a>b?(a>c?a:c):(b>c?b:c))
19 typedef long long LL;
20 typedef unsigned long long ULL;
21 const int INF = 0x3f3f3f3f;
22 const double PI = 4.0*atan(1.0);
23 
24 int n, t, ans;
25 typedef struct Interval{
26     int st, et;
27     bool operator<(const Interval &a) const{
28         return st < a.st;
29     }
30 }I;
31 I a[25005];
32 
33 bool solve()
34 {
35     int i = 0, et = 0, tmp;
36     ans = 0;
37     while (i < n&&et < t){
38         if (a[i].st>et + 1) return false;
39         tmp = -1;
40         while (i < n&&a[i].st <= et + 1){
41             tmp = MAX2(tmp, a[i].et); i++;
42         }
43         et = tmp;
44         ans++;
45     }
46     if (et < t) return false;
47     else return true;
48 }
49 
50 int main()
51 {
52     scanf("%d%d", &n, &t);
53         for (int i = 0; i < n; i++)
54             scanf("%d%d", &a[i].st, &a[i].et);
55     sort(a, a + n);
56     printf("%d\n", solve() ? ans : -1);
57 }