poj 1094 Sorting It All Out

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 6A<BA<CB<CC<DB<DA<B3 2A<BB<A26 1A<Z0 0

Sample Output

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

#include <iostream>#include <cstdio>#include <cstring>#include <queue>using namespace std;bool Map[50][50];int du[50];int n,m;queue<int >que;void Empty(){    while(!que.empty())        que.pop();}int Topo(){    int test[30];    int result = 1;    for(int i=1;i<=n;i++)        test[i] = du[i];    for(int i=1;i<=n;i++)    {        int cont = 0;        int pos;        for(int j=1;j<=n;j++)        {            if(test[j] == 0)            {                cont++;                pos = j;            }        }        if(cont == 0)            return 0;        if(cont > 1)            result = -1;        que.push(pos);        test[pos] = -1;        for(int j=1;j<=n;j++)        {            if(Map[pos][j])                test[j]--;        }    }    return result;}int main(){    //freopen("in.txt","r",stdin);    while(cin>>n>>m)    {        if(n == 0 && m == 0)            break;        memset(Map,false,sizeof(Map));        memset(du,0,sizeof(du));        char str[3];        bool flag = false;        int To;        for(int i=1;i<=m;i++)        {            Empty();            cin>>str;            if(flag)                continue;            int a = str[0] - 'A' + 1;            int b = str[2] - 'A' + 1;            Map[a][b] = true;            du[b]++;            To = Topo();            if(To == 0)            {                flag = true;                printf("Inconsistency found after %d relations.\n",i);            }            else if(To == 1)            {                flag = true;                printf("Sorted sequence determined after %d relations: ",i);                while(!que.empty())                {                    int t = que.front();                    printf("%c",t + 'A' - 1);                    que.pop();                }                printf(".\n");            }        }        if(To == -1)            printf("Sorted sequence cannot be determined.\n");    }    return 0;}