学步园

拓扑排序，判断是否可准确排序，或者存在环，或者无法准确排序

#include<stdio.h>
#include<string.h>
int n,m,cnt=1,in[30],g[30][30],tt[30];
char final[30];
int topo()
{
	int i,j,hash,done=0,num=0;
	int vis[30];
	memset(vis,0,sizeof(vis));
	final[n]='\0';
	while(1)
	{
		hash=0;
		for(i=1;i<=n;i++)
		{
			if(!vis[i]&&!in[i])
				if(!hash)
				{
					vis[i]=1;
					hash=i;
					final[n-num-1]=i+'A'-1;
					num++;
				}
				else {done=1;break;}
		}
		if(num==n)
		{
			if(done) return -1;			
			return 1;
		}
		if(!hash) return 2;
		if(hash)
		{
			for(j=1;j<=n;j++)
			{
				if(g[hash][j])
					in[j]-=g[hash][j];
			}
		}
	}
}
main()
{
	int i,ok,sign;
	char s[10];
	//freopen("D:\\o.txt","r",stdin);
	while(scanf("%d%d",&n,&m)&&n+m)
	{		
		sign=0;
		memset(tt,0,sizeof(tt));
		memset(g,0,sizeof(g));
		getchar();
		for(i=1;i<=m;i++)
		{
			gets(s);
			tt[s[0]-'A'+1]++;
			g[s[2]-'A'+1][s[0]-'A'+1]++;
			if(!sign)
			{
				memcpy(in,tt,sizeof(in));
				ok=topo();				
				if(ok==1)
				{
					sign=1;
					printf("Sorted sequence determined after %d relations: %s.\n",i,final);
				}
				else if(ok==2)
				{
					sign=1;
					printf("Inconsistency found after %d relations.\n",i);
				}
				else if(ok==-1&&m==i)
				{
					sign=1;
					printf("Sorted sequence cannot be determined.\n");
				}
			}
		}
	}
	return 0;
}