poj 1094 拓扑排序 是否是合法前行课

注意问题的转换，有环，无序，有序，还有他们的包含分界点

其中将字母装换成数字节点很妙

#include <stdio.h>
#include <string.h>

int map[27][27],indegree[27],q[27];

int n,m;

int topsort()
{
	int i,num,flag,j,start;

	int temp[27],c;

	c=0;

	flag=1;

	for(i=1;i<=n;i++)
		temp[i]=indegree[i];

	for(i=1;i<=n;i++)
	{
		num=0;
		for(j=1;j<=n;j++)
		{
			if(temp[j]==0)
			{
				num++;
				start=j;
			}
		}

		if(num==0)
			return 0;
		if(num>1)
			flag=-1;

		q[c++]=start;

		temp[start]=-1;

		for(j=1;j<=n;j++)
		{
			if(map[start][j]==1)
				temp[j]--;
		}
	}

	return flag;
}

int main()
{
	char str[4];

	int i,j,s;

	int singe;

	while(scanf("%d%d",&n,&m),n+m)
	{
		singe=0;

		memset(indegree,0,sizeof(indegree));
		memset(map,0,sizeof(map));

		for(i=1;i<=m;i++)
		{
			scanf("%s",str);

			if(singe)continue;

			int x=str[0]-'A'+1;
			int y=str[2]-'A'+1;
			map[x][y]=1;
			indegree[y]++;
			s=topsort();

			if(s==0)
			{
				printf("Inconsistency found after %d relations.\n",i);
				singe=1;
				continue;
			}

			if(s==1)
			{
				printf("Sorted sequence determined after %d relations: ",i);
				singe=1;
				for(j=0;j<n;j++)
                    printf("%c",q[j]+'A'-1);
                printf(".\n");
			}
		}
		if(!singe)
			printf("Sorted sequence cannot be determined.\n");
	}
	

	return 0;
}