poj1094

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;}