qzezoj 1667 Sorting It All Out

题面传送门
这个对于每个边跑拓扑序即可，如果有环那么不可行，如果两个字母拓扑序相同也不可行。
代码实现:

#include<cstdio>
#include<cstring>
#include<queue>
#include<algorithm>
using namespace std;
int n,m,k,x,y,z,in[139],flag,out[139],flags[139],sh,now,cur,pus,tot,topo[139];
struct yyy{int to,z;}tmp;
struct ljb{
    int head,h[139];
    yyy f[10039];
    inline void add(int x,int y){
        f[++head]=(yyy){y,h[x]};
        h[x]=head;
    }
}s;
char _s,sf,sss;
queue<int > q;
int main(){
    register int i,j;
    scanf("%d",&n);
    while(n){
        memset(s.h,-1,sizeof(s.h));
        memset(in,0,sizeof(in));
        s.head=pus=0;
        scanf("%d",&m);
        for(i=1;i<=m;i++){
            _s=getchar();
            while(_s<'A'||_s>'Z')_s=getchar();
            sss=getchar();
            sf=getchar();
            if(pus) continue;
            if(sss=='>') swap(sf,_s);
            s.add(_s-'A'+1,sf-'A'+1);
            in[sf-'A'+1]++;
            flag=sh=0;
            for(j=1;j<=n;j++) out[j]=in[j];
            for(j=1;j<=n;j++) if(!out[j]){q.push(j);topo[j]=1;}
            while(!q.empty()){
                now=q.front();
                q.pop();
                flags[++sh]=now;
                cur=s.h[now];
                while(cur!=-1){
                    tmp=s.f[cur];
                    out[tmp.to]--;
                    if(!out[tmp.to]) q.push(tmp.to),topo[tmp.to]=topo[now]+1;
                    cur=tmp.z;
                }
            }
            flag=0;
            for(j=1;j<=n;j++) if(out[j]) {flag=1;break;}
            if(flag){
                printf("Inconsistency found after %d relations.\n",i);
                pus=1;continue;
            }
            sort(topo+1,topo+n+1);
            for(j=2;j<=n;j++) if(topo[j]==topo[j-1]){flag=1;break;}
            if(!flag){
                printf("Sorted sequence determined after %d relations: ",i);
                for(j=1;j<=n;j++) putchar(flags[j]+'A'-1);
                printf(".\n");pus=1;continue;
            }
        }
        if(!pus) printf("Sorted sequence cannot be determined.\n");
        scanf("%d",&n);
    }
}