POJ1094[有向环 拓扑排序]

//
//  main.cpp
//  poj1094
//
//  Created by Candy on 9/11/16.
//  Copyright © 2016 Candy. All rights reserved.
//

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
const int N=30;
int n,m,ind[N],ch[N][N];
char tmp[5],topo[N];
int q[N];
int topoSort(){
    int flag=2;//only sorted
    int indt[N];
    for(int i=1;i<=n;i++) indt[i]=ind[i];
    for(int i=1;i<=n;i++){//printf("%d %d %d \n",i,ind[i],ch[i][0]);
        int zero=0,u=0;
        for(int j=1;j<=n;j++) if(indt[j]==0) zero++,u=j;
        if(zero==0) return 1;//circle
        if(zero>1) flag=3;//no sorted
        indt[u]--;
        topo[i-1]=(char)u+‘A‘-1;
        q[i-1]=u;
        for(int j=1;j<=ch[u][0];j++)
            indt[ch[u][j]]--;
    }
    return flag;
}
int main(int argc, const char * argv[]) {
    while(cin>>n>>m){
        if(n==0&&m==0) break;
        memset(ch,0,sizeof(ch));
        memset(ind,0,sizeof(ind));
        memset(topo,0,sizeof(topo));
        int sign=0;
        
        for(int i=1;i<=m;i++){
            scanf("%s",tmp);
            if(sign) continue;
            int x=tmp[0]-‘A‘+1,y=tmp[2]-‘A‘+1;
            ind[y]++;
            ch[x][++ch[x][0]]=y;
            int flag=topoSort();
            if(flag==1){sign=1;printf("Inconsistency found after %d relations.\n",i);}
            if(flag==2){
                sign=1;printf("Sorted sequence determined after %d relations: %s.\n",i,topo);
//                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) printf("Sorted sequence cannot be determined.\n");
    }
    return 0;
}