POJ1094 拓扑排序

 1 //Memory: 224K        Time: 0MS
 2 #include <iostream>
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <string>
 6 
 7 using namespace std;
 8 
 9 const int maxn = 26;
10 bool g[maxn][maxn];
11 int indegree[maxn];
12 int in[maxn];
13 int vis[maxn];
14 int flag;
15 int n, m;
16 int out[maxn];
17 string s;
18 int size;
19 int ans;
20 
21 int topologicalSort()
22 {
23     memset(vis, 0, sizeof(vis));
24     memcpy(in, indegree, sizeof(in));
25     size = 0;
26     flag = 0;
27     while (size < n){
28         int num = 0;
29         int next;
30         for (int i = 0; i < n; i++){
31             if (vis[i]) continue;
32             if (in[i] == 0) {
33                 num++;
34                 if (num > 1) break;
35                 next = i;
36             }
37         }
38         if (num == 0) return 0;
39         else {
40             out[size++] = next;
41             vis[next] = 1;
42             for (int i = 0; i < n; i++) {
43                 if ( g[next][i] && !vis[i] )
44                     in[i]--;
45             }
46             if (num > 1)
47                 flag = 1;
48         }
49     }
50     if (flag == 0) return 1;
51     else return 2;
52 }
53 
54 int main()
55 {
56     while (cin >> n >> m && n) {
57         memset(g, 0, sizeof(g));
58         memset(indegree, 0, sizeof(indegree));
59         ans = 2;
60         for (int i = 0; i < m; i++){
61             cin >> s;
62             if ( ans != 2 ) continue;
63             if (!g[s[0] - ‘A‘][s[2] - ‘A‘]) {
64                 g[s[0] - ‘A‘][s[2] - ‘A‘] = 1;
65                 indegree[s[2] - ‘A‘]++;
66                 ans = topologicalSort();
67 
68                 if (ans == 0) {
69                     cout << "Inconsistency found after " << i + 1 <<" relations." << endl;
70                 }
71                 else if ( ans == 1 ){
72                     cout << "Sorted sequence determined after " << i + 1 << " relations: ";
73                     for (int i = 0; i < n; i++)
74                         cout << (char)(out[i] + ‘A‘);
75                     cout << "." << endl;
76                 }
77             }
78         }
79         
80         if ( ans == 2 )
81             cout << "Sorted sequence cannot be determined." << endl;
82     }
83     return 0;
84 }