POJ 1094 Sorting It All Out（topsort Language: Sorting It All Out Time Limit: 1000MSMemory Limit: ）

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Sorting It All Out

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 28241 Accepted: 9757

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.

Source

East Central North America 2001

解释在代码中：

#include<iostream>#include<cstring>#include<algorithm>#include<cstdio>#include<queue>#include<stack>using namespace std;#define N 300int a[N][N],d[N];int ans[N];int n,m;int topsort(){int i,j=0;int in[N];memcpy(in,d,sizeof(d));      //注意把入度复制到另外一个数组    stack<int>q;for(i=1;i<=n;i++)if(in[i]==0)q.push(i);int x,flag=0;while(!q.empty()){      if(q.size()>1) flag=1;  x=q.top();  q.pop();  ans[j++]=x;  for(i=1;i<=n;i++)if(a[x][i])  {  if(--in[i]==0)q.push(i);  }}if(j!=n) return 2;if(flag) return 0;return 1;}void print(){int i;for(i=0;i<n;i++)printf("%c",ans[i]+'A'-1);printf(".\n");}int main(){    int i,j,yes,cut;    char x,y;    while(scanf("%d%d",&n,&m),n+m){        getchar();    memset(a,0,sizeof(a));memset(d,0,sizeof(d));        yes=0;for(i=1;i<=m;i++){scanf("%c<%c",&x,&y);getchar();if(a[x-'A'+1][y-'A'+1])               continue;            if(yes) continue;    a[x-'A'+1][y-'A'+1]=1;d[y-'A'+1]++;yes=topsort();if(yes)cut=i;} if(yes==1){printf("Sorted sequence determined after %d relations: ",cut);print();}            elseif(yes==2){printf("Inconsistency found after %d relations.\n",cut);i=n+1;}else            if(yes==0)printf("Sorted sequence cannot be determined.\n");}return 0;}