poj Sorting It All Out 托普排序

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<cstdio>#include<iostream>#include<algorithm>#include<cstring>#include<queue>#include<string.h>using namespace std;struct node{    int v,next;} edge[200000];int n,m,cnt,head[20000],rudu[2000];void add(int u,int v){    edge[cnt].v=v;    edge[cnt].next=head[u];    head[u]=cnt++;}int sh[20000],k;int  topu(){    int flag1=0;    k=0;    int rd[2000];    memcpy(rd,rudu,sizeof(rudu));    queue<int>q;    for(int i=1; i<=n; i++)        if(!rd[i])        {            q.push(i);        }    while(!q.empty())    {        int t=q.front();        sh[k++]=t;        q.pop();        if(!q.empty())        {            flag1=1;        }        for(int pp=head[t]; pp!=-1; pp=edge[pp].next)        {            rd[edge[pp].v]--;            if(rd[edge[pp].v]==0)                q.push(edge[pp].v);        }    }    if(k!=n)        return 1;    else if(flag1==1)        return 2;    return 0;}int main(){    char a,b,c;    while(scanf("%d %d",&n,&m),n||m)    {        getchar();        memset(head,-1,sizeof(head));        memset(rudu,0,sizeof(rudu));        int x=0;        for(int i=1; i<=m; i++)        {            cin>>a>>b>>c;            int a1,c1;            a1=a-'A'+1;            c1=c-'A'+1;            if(x==0)            {                    add(a1,c1);                    rudu[c1]++;                int s=topu();                if(s==0)                {                    printf("Sorted sequence determined after %d relations: ",i);                    for(int j=0; j<k; j++)                        printf("%c",sh[j]+'A'-1);                    printf(".\n");                    x=1;                }                else if(s==1)                {                    printf("Inconsistency found after %d relations.\n",i);                     x=1;                }            }        }        if(!x)        {            cout<<"Sorted sequence cannot be determined."<<endl;        }    }    return 0;}