有向圖找環

 1 #include<cstdio>
 2 #include<cstring>
 3 int map[27][27],indegree[27],q[27];
 4 int TopoSort(int n){
 5     int t=0,temp[27],p,m,flag=1;  //flag=1:有序 flag=-1:不確定
 6     for(int i=1;i<=n;i++)temp[i]=indegree[i];
 7     for(int i=1;i<=n;i++){
 8         m=0;for(int j=1;j<=n;j++)if
 
(temp[j]==0)m++,p=j;//查詢入度為零的頂點個數
 9         if(m==0)return 0; //有環
10         if(m>1) flag=-1;  //無序
11         q[++t]=p,temp[p]=-1;//入度為零的點入隊
12         for(int j=1;j<=n;j++)if(map[p][j]==1)temp[j]--;
13     }
14     return flag;
15 }
16 int main(){
17     int n,m,sign,x,y;
18     for(char s[5];scanf("%d%d
 
",&n,&m)!=EOF;){
19         if(n==0&&m==0)break;
20         memset(map,0,sizeof(map)),sign=0;
21         memset(indegree,0,sizeof(indegree));
22         for(int i=1;i<=m;i++){
23             scanf("%s",s);
24             if(sign)continue;
25             x=s[0]-'A'+1,y=s[2]-'A'+1;
26             map[x][y]=1
 
,indegree[y]++;
27             int f=TopoSort(n);
28             if(f==0)sign=1,printf("Inconsistency found after %d relations.\n",i);
29             if(f==1){
30                 sign=1,printf("Sorted sequence determined after %d relations: ",i);
31                 for(int j=1;j<=n;j++)printf("%c",q[j]+'A'-1);
32                 puts(".");
33             }
34         }
35         if(!sign)puts("Sorted sequence cannot be determined.");
36     }
37     return 0;
38 }

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <iostream>
 4 #include <algorithm>
 5 using namespace std;
 6 const int N = 30;
 7 int n, m, d[N][N], e[N][N];
 8  
 9 int floyd() {
10     memcpy(e, d, sizeof(e));
11     for (int k = 0; k < n; k++)
12         for (int i = 0; i < n; i++)
13             for (int j = 0; j < n; j++) {
14                 e[i][j] |= e[i][k] & e[k][j];
15                 if (e[i][j] == e[j][i] && e[i][j] && i != j) return -1;
16             }
17     for (int i = 0; i < n; i++)
18         for (int j = 0; j < n; j++)
19             if (e[i][j] == e[j][i] && !e[i][j] && i != j) return 0;
20     return 1;
21 }
22  
23 void Sorting_It_All_Out() {
24     memset(d, 0, sizeof(d));
25     bool flag = 1;
26     for (int i = 1; i <= m; i++) {
27         char s[6];
28         scanf("%s", s);
29         d[s[0]-'A'][s[2]-'A'] = 1;
30         if (flag) {
31             int now = floyd();
32             if (now == -1) {
33                 printf("Inconsistency found after %d relations.\n", i);
34                 flag = 0;
35             } else if (now == 1) {
36                 printf("Sorted sequence determined after %d relations: ", i);
37                 pair<int, char> ans[N];
38                 for (int j = 0; j < n; j++) {
39                     ans[j].first = 0;
40                     ans[j].second = 'A' + j;
41                 }
42                 for (int j = 0; j < n; j++)
43                     for (int k = 0; k < n; k++)
44                         if (e[j][k]) ++ans[j].first;
45                 sort(ans, ans + n);
46                 for (int j = n - 1; j >= 0; j--) printf("%c", ans[j].second);
47                 puts(".");
48                 flag = 0;
49             }
50         }
51     }
52     if (flag) puts("Sorted sequence cannot be determined.");
53 }
54  
55 int main() {
56     while (cin >> n >> m && n) Sorting_It_All_Out();
57     return 0;
58 }