POJ1094 Sorting It All Out 拓扑排序 入度（注意优先级）

Sorting It All Out

Time Limit: 1000MS Memory Limit: 10000K
Total Submissions: 40917 Accepted: 14342
Description

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.
Source

East Central North America 2001

注意优先级的选择

Inconsistency found ：出现环后立刻跳出循环。
Sorted sequence cannot be determined ：加入所有边后输出。
Sorted sequence determined： 全部排序确定后输出。

代码如下：

#include <iostream>
#include <cstdio>
#include <cmath>
#include <set>
#include <string>
#include <queue>
#include <map>
#include <vector>
#include <cstring>
#include <algorithm>
#include <sstream>
#define INF 10000000
#define MAXN 2e5+9
const long long mod=1e6+3;
using namespace std;
int in[50];
int via[50];
vector<int> vec[50];
void mclear(queue<int> &q)
{
    queue<int> e;
    swap(e,q);
}
void init()
{
    for(int i=0;i<27;i++)
    {
        vec[i].clear();
    }
}
//queue<int> ans;
int main()
{
    int n,m;
    while (scanf("%d%d",&n,&m)==2 && (m||n))
    {
        init();
        int i,j,k;
        int f=0;
        char c[5];
        for(i=1;i<=m;i++)
        {
            //memset(via,0,sizeof(via));
            memset(in,0,sizeof(in));
            scanf("%s",c);
            //cout << c <<endl;
            if(f==1 || f==3) continue;
            vec[c[0]-'A'].push_back(c[2]-'A');
            for(j=0;j<n;j++)
            {
                //cout << j << "   ";
                for(k=0;k<vec[j].size();k++)
                {
                  //  cout << vec[j][k] <<' ';
                    in[vec[j][k]]++;
                }
                //cout << endl;
            }
            for(j=0;j<n;j++)
            {
                //cout << in[j] <<' ';
            }
           // cout << endl;
            int num=n;
            queue<int> q;
            if(f==2) f=0;
            while (num>0)
            {
                int cnt=0;
                for(j=0;j<n;j++)
                {
                    if(in[j]==0) cnt++;
                }
             //   if(i==4) cout << cnt << endl;
                if(cnt==0)
                {
                    f=1;
                    break;
                }
                if(cnt>1)
                {
                    f=2;
                }
                for(j=0;j<n;j++)
                {
                    if(in[j]==0)
                    {
                        num--;
                        q.push(j);
                        in[j]=-1;
                        for(k=0;k<vec[j].size();k++)
                        {
                            in[vec[j][k]]--;
                        }
                        break;
                    }
                }
            }
            if(f!=1 && f!=2) f=3;
            if(f==1)
            {
                cout <<"Inconsistency found after "<< i <<" relations."<<endl;
            }
            if(f==3)
            {
                cout <<"Sorted sequence determined after "<< i <<" relations: ";
                while (!q.empty())
                {
                    cout << (char)(q.front()+'A');
                    q.pop();
                }
                cout << '.'<<endl;
            }
        }
        if(f==2)
        {
            cout << "Sorted sequence cannot be determined."<<endl;
        }
    }
    return 0;
}