三部曲一(数据结构)-1011-Sorting It All Out

每次加入一个关系都要进行拓扑排序，不过在排序过程中需要判断是否出现多个入度为0的点，如果出现了就说明不能确定大小关系。不论出不出现多个入度为0的点拓扑排序都要进行到最后来判断是否出现环，因为一旦出现环就不用再比了，一定是不能排序的。

另外，注意输出序列之后的那个逗号。。。。。。

Sorting It All Out

Time Limit : 2000/1000ms (Java/Other)   Memory Limit : 20000/10000K (Java/Other)

Total Submission(s) : 24   Accepted Submission(s) : 13

Problem 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

PKU

#include <iostream>
#include <cstring>
#include <stdio.h>
#define inf 0xfffffff
#define maxn 27

using namespace std;

int n,m;
char les,first,second;
int mp[maxn][maxn],ans[maxn];

int topo()
{
    int i,j,res=0;
    int into[maxn]={0};
    for(i=0;i<n;i++)
    {
        for(j=0;j<n;j++)
        {
            if(mp[i][j]>0)
                into[j]++;
        }

    }
    for(i=0;i<n;i++)
    {
        int cnt=0,tmp=-1;
        for(j=0;j<n;j++)
        {
            if(into[j]==0)
            {
                cnt++;
                tmp=j;
            }
        }
        if(cnt==0)
            return 1;
        if(cnt>1)
            res=2;
        ans[i]=tmp;
        into[tmp]=-1;
        for(j=0;j<n;j++)
        {
            if(mp[tmp][j]>0)
                into[j]--;
        }
    }
    if(res==2)
        return 2;
    else
        return 3;
}

int main()
{
//    freopen("in.txt","r",stdin);
    while(cin>>n>>m&&(n+m))
    {
        memset(mp,0,sizeof(mp));
        memset(ans,0,sizeof(ans));
        int i,tp=2,last=0,num=0;
        for(i=0;i<m;i++)
        {
            cin>>first>>les>>second;
            int a=first-'A',b=second-'A';
            mp[a][b]=1;
            if(tp==2)
            {
                tp=topo();
            }
            if(last==2&&(tp==1||tp==3))
            {
                num=i+1;
            }
            last=tp;
        }
        if(tp==3)
        {
            cout<<"Sorted sequence determined after "<<num<<" relations: ";
            for(i=0;i<n;i++)
                cout<<char(ans[i]+'A');
            cout<<'.';
            cout<<endl;
        }
        else if(tp==2)
            cout<<"Sorted sequence cannot be determined."<<endl;
        else if(tp==1)
            cout<<"Inconsistency found after "<<num<<" relations."<<endl;

    }
    return 0;
}