zoj 1060 Sorting It All Out(拓扑排序)

#include<bits/stdc++.h>
using namespace std;

vector< vector<char> >v;
int n,m,use[30],cnt[30];
char ans[30],s[10];

int topsort(int x)
{
int i,j,t[30],f=1,r,c;
memset(ans,0,sizeof(ans));
for(i=0; i<30; i++) t[i]=cnt[i];
c=0;
r=0;
while(x--)
{
c=0;
for(i=0; i<n; i++)
{
if(t[i]==0)
{
j=i;
c++;
}
}
if(c>=1)
{
if(c>1) f=0;
for(i=0; i<v[j].size(); i++)
{
t[v[j][i]]--;
}
ans[r++]=j+'A';
t[j]=-1;
ans[r]=0;
}
else if(c==0)
return -1;
}
if(f)
return r;
else
return 0;
}

int main()
{
int flag,i,num,ok,k;
while(~scanf("%d%d",&n,&m))
{
if(n==0&&m==0) break;
v.clear();
v.resize(n);
memset(use,0,sizeof(use));
memset(cnt,0,sizeof(cnt));
ok=0;
num=0;
for(i=0; i<m; i++)
{
scanf("%s",s);
cnt[s[2]-'A']++;
v[s[0]-'A'].push_back(s[2]-'A');
if(!use[s[0]-'A'])
{
num++;
use[s[0]-'A']=1;
}
if(!use[s[2]-'A'])
{
num++;
use[s[2]-'A']=1;
}
if(ok==0)
{
int t=topsort(num);
if(t==n)
{
ok=1;
k=i+1;
}
else if(t==-1)
{
ok=-1;
k=i+1;
}
}
}
if(!ok) printf("Sorted sequence cannot be determined.\n");
else if(ok==1) printf("Sorted sequence determined after %d relations: %s.\n",k,ans);
else printf("Inconsistency found after %d relations.\n",k);
}
return 0;
}