pku 1094

pku 1094

#include < iostream >
using   namespace  std;
#define  M 26
bool  grap[M + 1 ][M + 1 ];
int  squ[M + 1 ];
char  equ[M * M][ 4 ];
int  ind[M + 1 ];
int  indcop[M + 1 ];
int  cnt,n,m;

int  topsort()
{
    int i,j,p,num=0,
        flag=0,
        now=0;
    for(i=0;i<n;i++)
        indcop[i]=ind[i];

    for(i=0;i<n;i++)   
    {       
        num=0;     
        for(j=0;j<n;j++)   
            if(indcop[j]==0)  
            {           
                num++;    
                p=j;       
            }       
            if(num==0)          //有回路        
                return 0;     
            if(num>1)           //不确定     
                flag=1;
                //return -1; //不确定的情况下还要判断有没回路，o(╯□╰)o
            indcop[p]=-1;           //置为负值   
            squ[now++]=p;   
            for(j=0;j<n;j++)     //删除相关的边       
                if(grap[p][j])         
                    indcop[j]--;   
    }    
    if(flag)       return -1; //不确定
    return 1;
}


int  main()
{
    int i,j,ret;
    char l,r;
    bool done;
    while(scanf("%d%d",&n,&m)==2 && n )
    {
        for(i=0;i<m;i++)
            scanf(" %s",&equ[i]);
        done=false;
        memset(ind,0,sizeof(ind));
        memset(grap,0,sizeof(grap));
        for(i=0;i<m;i++)
        {
            l=equ[i][0];r=equ[i][2];
            grap[l-'A'][r-'A']=true;
            ind[r-'A']++;
            ret=topsort();
            if( ret==0 ) { printf("Inconsistency found after %d relations.\n",i+1); done=true; break;}
            if( ret==1)
            {
                printf("Sorted sequence determined after %d relations: ",i+1);
                for(j=0;j<n;j++)
                    printf("%c",'A'+squ[j]);
                printf(".\n");
                done=true;
                break;
            }
        }
        if(!done) printf("Sorted sequence cannot be determined.\n");    
    }
    return 0;
}