Sorting It All Out (拓扑排序+思维)

An ascending sorted sequence of distinct values is one in which some form of a less-than operator is used to order the elements from smallest to largest. For example, the sorted sequence A, B, C, D implies that A < B, B < C and C < D. in this problem, we will give you a set of relations of the form A < B and ask you to determine whether a sorted order has been specified or not.

Input

Input consists of multiple problem instances. Each instance starts with a line containing two positive integers n and m. the first value indicated the number of objects to sort, where 2 <= n <= 26. The objects to be sorted will be the first n characters of the uppercase alphabet. The second value m indicates the number of relations of the form A < B which will be given in this problem instance. Next will be m lines, each containing one such relation consisting of three characters: an uppercase letter, the character "<" and a second uppercase letter. No letter will be outside the range of the first n letters of the alphabet. Values of n = m = 0 indicate end of input.

Output

For each problem instance, output consists of one line. This line should be one of the following three:

Sorted sequence determined after xxx relations: yyy...y. 
Sorted sequence cannot be determined. 
Inconsistency found after xxx relations.

where xxx is the number of relations processed at the time either a sorted sequence is determined or an inconsistency is found, whichever comes first, and yyy...y is the sorted, ascending sequence.

Sample Input

4 6
A<B
A<C
B<C
C<D
B<D
A<B
3 2
A<B
B<A
26 1
A<Z
0 0

Sample Output

Sorted sequence determined after 4 relations: ABCD.
Inconsistency found after 2 relations.
Sorted sequence cannot be determined.
代码：

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
#include<stack>
#include<vector>
#include<map>
#include<cmath>
const int maxn=1e5+;
typedef long long ll;
using namespace std;
vector<int>vec[];
int n,m;
int du[];
int chu[];
int du1[];
int flag;
vector<int>ans1;
void Tpsort()
{
    priority_queue<int,vector<int>,greater<int> >q;
    priority_queue<int>q1;

    int s=;
    for(int t=;t<n;t++)
    {
        if(chu[t]==&&du[t]==)
        {
         s=;
        }
    }
    for(int t=;t<n;t++)
    {
        du1[t]=du[t];
    }
    for(int t=;t<n;t++)
    {
        if(du1[t]==)
        {
            q.push(t);
            q1.push(t);
        }
    }
    vector<int>ans,ans2;
    while(!q.empty())
    {
        int now=q.top();
        int now2=q1.top();
        q.pop();
        q1.pop();
        ans.push_back(now);
        ans2.push_back(now2);
        for(int t=;t<vec[now].size();t++)
        {
            int next=vec[now][t];
            du1[next]--;
            if(du1[next]==)
            {
                q.push(next);
                q1.push(next);
            }
        }
    }
    if(ans.size()!=n)
    {
        flag=;
    }
//    cout<<ans.size()<<" "<<s<<endl;

    if(ans.size()==n&&s==)
    {
        int sss=;
        for(int t=;t<ans.size();t++)
        {
            if(ans[t]!=ans2[t])
            {
                sss=;
            }
        }
        if(sss==)
        {
            flag=;
            for(int t=;t<ans.size();t++)
            {
                ans1.push_back(ans[t]);
            }
        }

    }

}
int main()
{ 

   while(cin>>n>>m)
   {
    if(n==&&m==)
    {
        break;
    }
    for(int t=;t<n;t++)
    {
        vec[t].clear();
    }
       char str[];
       memset(du,,sizeof(du));
       memset(chu,,sizeof(chu));
       flag=;
       int ss=;
       int k;
       ans1.clear();
       for(int t=;t<=m;t++)
       {
           scanf("%s",str);
           vec[str[]-'A'].push_back(str[]-'A');
           du[str[]-'A']++;
           chu[str[]-'A']++;
           if(ss)
           {
           continue;
        }
           Tpsort();
           if(flag==)
           {
               printf("Inconsistency found after %d relations.\n",t);
               ss=;
        }
        else if(flag==)
        {
            ss=;
            printf("Sorted sequence determined after %d relations: ",t);
            for(int j=;j<n;j++)
            {
                printf("%c",ans1[j]+'A');
            }
            printf(".\n");

        }
    }
    if(ss==)
    puts("Sorted sequence cannot be determined.");

   }
   return ;
}