hdoj-2647-Reward(拓扑排序)

题目链接:

 1 /*
 2     Name:hdoj-2647-Reward
 3     Copyright:
 4     Author:
 5     Date: 2018/4/11 15:59:18
 6     Description:
 7 */
 8 #include <iostream>
 9 #include <queue>
10 #include <vector>
11 #include <cstring>
12 #include <algorithm>
13 using namespace std;
14 const int MAXN = 1e+5;
15 int du[MAXN], n , m, L[MAXN];
16 vector<int>  g[MAXN];
17 bool topsort() {
18     memset(du, 0, sizeof(du));
19     for (int i=0; i<n; i++) {
20         for (int j=0; j<g[i].size(); j++) {
21             du[g[i][j]]++; 
22         }
23     }
24     int tot = 0;
25     queue<int> Q;
26     for (int i=0; i<n; i++) {
27         if (!du[i]) {
28             Q.push(i);
29             L[i] = 0;
30         }
31     }
32     while (!Q.empty()) {
33         int x = Q.front();
34         Q.pop();
35         tot++;
36         for (int j=0; j<g[x].size(); j++) {
37             int t = g[x][j];
38             du[t]--;
39             if (!du[t]) {
40                 Q.push(t);
41                 L[g[x][j]] = L[x] + 1;
42             }
43         } 
44     }
45     if (tot == n) return 1;
46     return 0;
47 } 
48 int main()
49 {
50 //    freopen("in.txt", "r", stdin);
51     while (cin>>n>>m && (m || n)) {
52         memset(L, 0, sizeof(L));
53         memset(g, 0, sizeof(g));
54         for (int i=0; i<m; i++) {
55             int a, b;
56             cin>>a>>b;
57             a--;
58             b--;
59             g[b].push_back(a);
60         }
61         if (topsort() == 1) {
62             int sum = 0;
63             for (int i=0; i<n; i++) {
64                 sum += L[i];
65             }
66             cout<<sum+n*888<<endl;
67         }
68         else cout<<"-1"<<endl;
69     }
70     return 0;
71 }

 

posted @ 2018-04-11 17:41  朤尧  阅读(237)  评论(0编辑  收藏  举报