Sorting In All Out

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

 

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.

 

      先不说怎么做了，这题一个毛病是输出不是在输入完之后，而是可能才输入了一部分数据就输出了！第一次见这种操作，什么毛病，搞不明白。这是个拓扑排序的问题，但是我按拓扑入栈出栈的一套写不对，这个题的三种情况我判断不全。然后看了看人家的做法，感觉这一个可以当做拓扑排序的另一个模板来记住，是用于判断能不能得到一个确定的结果。（原来的拓扑排序出来是可能排出来好几种，比方a<b,a<c,b<d,c<d,可以排出）。下面是代码：

#include<iostream>#include<cstring>#include<string>using namespace std;int n,m;int r[30],c[30];int p[30][30];int ans[30];  //存排序结果int ioan(){    int flag=1;    int cnt=0;    int rr[30];    int cc[30];    for(int i=1;i<=n;i++)//用cc【】、rr【】，防止更改数据    {        rr[i]=r[i];        cc[i]=c[i];    }    for(int i=1;i<=n;i++)    {        int r0=0,k=0;        for(int j=1;j<=n;j++)        {            if(rr[j]==0)            {                r0++;                k=j;            }        }        if(r0==0)        {            flag=0;            return flag;  //表明有环  直接  return        }        if(r0>1)      //表明无序        {            flag=-1;        }        cnt++;        ans[cnt]=k;  //存入 k        rr[k]=-1;    //标记 k        for(int j=1;j<=cc[k];j++)        {            int y=p[k][j];            rr[y]--;        }    }    return flag;    //最后return flag    等于-1则无序      等于1则表示排完了}int main(){    char a,b;    int x,y;    while(cin>>n>>m)    {        if(n==0 && m==0)            break;        int flag=0;        memset(r,0,sizeof(r));        memset(c,0,sizeof(c));        memset(p,0,sizeof(p));        for(int i=1;i<=m;i++)        {            cin>>a>>b>>b;            if(flag==1)            {                continue;            }            x=a-'A'+1;            y=b-'A'+1;            c[x]++;            p[x][c[x]]=y;            r[y]++;            int f=ioan();            if(f==0)            {                flag=1;                cout<<"Inconsistency found after "<<i<<" relations."<<endl;            }            if(f==1)            {                flag=1;                cout<<"Sorted sequence determined after "<<i<<" relations: ";                for(int i=1;i<=n;i++)                    cout<<char(ans[i]+'A'-1);                cout<<"."<<endl;            }        }        if(flag==0)            cout<<"Sorted sequence cannot be determined."<<endl;    }    return 0;}