POJ1094 Sorting It All Out

#include<iostream>
#include<algorithm>
#include<cstring>
#include<vector>
#include<queue>
const int N=26;
using namespace std;
struct d{
    char a,b,c;
}oj[100000];
int in[N],tin[N],ans[N],len;
vector<int>p[N];
int n,m,k;
int topo(){
    queue<int>q;
    k=0;
    memset(tin,0,sizeof(tin));
    for(int i=0;i<n;i++) if(!in[i]) {q.push(i);}
    int flag=0;
    len=0;
    while(!q.empty()){
        if(q.size()>1) flag=1;
        int t=q.front();q.pop();
        ans[k++]=t;
        for(int i=0;i<p[t].size();i++){
            int s=p[t][i];
            if(++tin[s]==in[s]){
                q.push(s);
            }
        } 
    }
    if(k<n) return -1; 
    else if(flag) return 0;
    return 1; 
}
int main(){
    while(cin>>n>>m&&(n+m)){
        for(int i=0;i<N;i++) p[i].clear();
        memset(in,0,sizeof(in));
        for(int i=0;i<m;i++){
            cin>>oj[i].a>>oj[i].b>>oj[i].c;
        }   
        int hl=-1,ul=-1;    
        for(int i=0;i<m;i++){
            int x=oj[i].a-‘A‘, y=oj[i].c-‘A‘;
            if(oj[i].b==‘>‘){
                p[x].push_back(y);
                in[y]++;
            }
            else if(oj[i].b==‘<‘){
                p[y].push_back(x);
                in[x]++;
            }
            int t=topo();
            if(t==1){
                hl=i+1;
                break;
            }
            else if(t==-1){
                 ul=i+1;
                 break;
            }
        }
        if(hl!=-1){
            cout<<"Sorted sequence determined after "<<hl<<" relations: ";
            for(int i=n-1;i>=0;i--) putchar(‘A‘+ans[i]);cout<<‘.‘;
        }
        else if(ul!=-1){
            cout<<"Inconsistency found after "<<ul<<" relations.";
        }
        else cout<<"Sorted sequence cannot be determined.";
        cout<<endl;
    }
    return 0;
}