zoj1060

拓扑排序题目

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
char ch[50];
int n,m,du[30],G[30][30],tmp[30],vis[30];

int solve()
{
  memcpy(tmp,du,sizeof(du));
  memset(vis,0,sizeof(vis));
  int flag=1;
  for(int i=0;i<n;i++)
  {
    int s=-1,cnt=0;
    for(int j=0;j<n;j++)
    {
      if(!vis[j]&&!tmp[j])
      {
        s=j;cnt++;
      }
    }
    if(cnt!=1)
    {
      flag=cnt;
      if(flag==0)
        break;
    }
    ch[i]='A'+s;
    vis[s]=1;
    for(int j=0;j<n;j++)
      if(!vis[j]&&G[s][j])
        tmp[j]--;
  }
  ch[n]=0;
  if(flag==0)  return 0;
  if(flag==1)  return 1;
  return 2;
}

int main()
{
  char copy[50];
  int mark1,mark2;
  while(scanf("%d%d",&n,&m))
  {
    if(m==0&&n==0)
      break;
    mark1=mark2=0;
    memset(G,0,sizeof(G));
    memset(du,0,sizeof(du));
    int s=2,flag=0;
    for(int i=0;i<m;i++)
    {
      scanf("%s",ch);
      if(flag)  continue;
      int u=ch[0]-'A';
      int v=ch[2]-'A';
      G[u][v]=1;
      du[v]++;
      s=solve();
      if(s==2)  continue;
      if(s==1)  
      {
        mark1=i+1;
        strcpy(copy,ch);
        flag = 1;
      }
      else
      {
        mark2=i+1;
        flag = 1;
      }
    }
    if(mark1)
    {
      printf("Sorted sequence determined after %d relations: %s.\n",mark1,copy);
    }
    if(mark2)
    {
      printf("Inconsistency found after %d relations.\n",mark2);
    }
    if(s==2)
    {
      puts("Sorted sequence cannot be determined.");
    }
  }
  return 0;
}