hdu 2647 Reward (topsort)

 1 #include <map>
 2 #include <queue>
 3 #include <cmath>
 4 #include <vector>
 5 #include <string>
 6 #include <cstdio>
 7 #include <cstring>
 8 #include <climits>
 9 #include <iostream>
10 #include <algorithm>
11 #define INF 0xffffff
12 using namespace std;
13 
14 const int my_max = 20010;
15 int n, m, a, b, my_cnt, my_indeg[my_max];
16 vector <int> my_G[my_max];
17 
18 int topsort()
19 {
20     my_cnt = 0;
21     int my_ans = 0, t = 887;
22     queue <int> Q;
23     while (t ++)
24     {
25         int flag = -1, my_temp = 0;
26         for (int i = 1; i <= n; ++ i)
27             if (my_indeg[i] == 0)
28             {
29                 my_indeg[i] = -1;
30                 flag = 1;
31                 Q.push(i);
32                 my_cnt ++;
33                 my_temp ++;
34             }
35 
36         if (flag == -1) break;
37         my_ans += my_temp * t;
38 
39         while (my_temp --)
40         {
41             int my_now = Q.front();
42             for (int i = 0; i < my_G[my_now].size(); ++ i)
43                 my_indeg[my_G[my_now][i]] --;
44             my_G[my_now].clear();
45             Q.pop();
46         }
47     }
48     if (my_cnt == n)
49         return my_ans;
50 
51     for (int i = 1; i <= n; ++ i)
52         my_G[i].clear();
53     return -1;
54 }
55 
56 int main()
57 {
58     while (~scanf("%d%d", &n, &m))
59     {
60         memset(my_indeg, 0, sizeof(my_indeg));
61         while (m --)
62         {
63             scanf("%d%d", &a, &b);
64             ++ my_indeg[a];
65             my_G[b].push_back(a);
66         }
67 
68         printf("%d\n", topsort());
69     }
70     return 0;
71 }