poj 1094

Sorting It All Out

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 26911		Accepted: 9285

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

field=source&key=East+Central+North+America+2001" style="text-decoration:none">East Central North America 2001

AC代码：

#include<iostream>

#include<vector>

#include<stack>

#include<algorithm>

#include<cstring>

#include<stdio.h>

using namespace std;

int n,m;

int in[30],tmp_in[30];

int f1,f2;

int str[30];

vector <int> G[30];

void top_sort(){                //拓扑排序

    f1=0;             //没有环

    f2=1;             //唯一排序

    for(int i=0;i<n;i++)

        tmp_in[i]=in[i];

    stack <int> s;

    while(!s.empty())

        s.pop();

    for(int i=0;i<n;i++)

        if(tmp_in[i]==0)

            s.push(i);

    int counter=0;

    while(!s.empty()){

        if(s.size()>=2){

            f2=0;

        }

        int tmp=s.top();

        s.pop();

        str[counter++]=tmp;

        for(int i=0;i<G[tmp].size();i++){

            tmp_in[G[tmp][i]]--;

            if(!tmp_in[G[tmp][i]])

                s.push(G[tmp][i]);

        }

    }

    if(counter<n)

        f1=1;

}

int main(){

    while(cin>>n>>m&&(n!=0||m!=0)){

        memset(in,0,sizeof(in));

        int i;

        for(i=0;i<n;i++)

            if(!G[i].empty())

                G[i].clear();

        for(i=0;i<m;i++){

            char ch[5]; cin>>ch;

            G[ch[0]-'A'].push_back(ch[2]-'A');

            in[ch[2]-'A']++;

            top_sort();

            if(f1){

                cout<<"Inconsistency found after "<<i+1<<" relations."<<endl;

                for(int j=i+1;j<m;j++)    //注意这里要输入剩下的信息才干退出

                    cin>>ch;

                break;

            }

            else if(f2){

                cout<<"Sorted sequence determined after "<<i+1<<" relations: ";

                for(int j=0;j<n;j++)

                    cout<<char (str[j]+'A');

                cout<<'.'<<endl;

                for(int j=i+1;j<m;j++)      //注意这里要输入剩下的信息才干退出

                    cin>>ch;

                break;

            }

        }

        if(i>=m)

            cout<<"Sorted sequence cannot be determined."<<endl;

    }

    return 0;

}

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