POJ1094(拓扑排序判定有环、不能确定、能确定)
#include<stdio.h>
#include<string.h>
int map[27][27],indegree[27],q[27];
int TopoSort(int n) //拓扑排序
{
int c=0,temp[27],loc,m,flag=1,i,j; ////flag=1:有序 flag=-1:不确定
for(i=1;i<=n;i++)
temp[i]=indegree[i];
for(i=1;i<=n;i++)
{
m=0;
for(j=1;j<=n;j++)
if(temp[j]==0) { m++; loc=j; } //查找入度为零的顶点个数
if(m==0) return 0; //有环
if(m>1) flag=-1; // 无序
q[c++]=loc; //入度为零的点入队
temp[loc]=-1;
for(j=1;j<=n;j++)
if(map[loc][j]==1) temp[j]--;
}
return flag;
}
int main()
{
int m,n,i,sign; //当sign=1时,已得出结果
char str[5];
while(scanf("%d%d",&n,&m))
{
if(m==0&&n==0) break;
memset(map,0,sizeof(map));
memset(indegree,0,sizeof(indegree));
sign=0;
for(i=1;i<=m;i++)
{
scanf("%s",str);
if(sign) continue; //一旦得出结果,对后续的输入不做处理
int x=str[0]-'A'+1;
int y=str[2]-'A'+1;
map[x][y]=1;
indegree[y]++;
int s=TopoSort(n);
if(s==0) //有环
{
printf("Inconsistency found after %d relations.\n",i);
sign=1;
}
if(s==1) //有序
{
printf("Sorted sequence determined after %d relations: ",i);
for(int j=0;j<n;j++)
printf("%c",q[j]+'A'-1);
printf(".\n");
sign=1;
}
}
if(!sign) //不确定
printf("Sorted sequence cannot be determined.\n");
}
return 0;
}