POJ1094 Sorting It All Out
Time Limit: 1000MS Memory Limit: 10000K
Total Submissions: 18073 Accepted: 6145
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.
*******************************************************************
拓扑排序，第一次写，可惜不是一A是二A，5555.
#include<iostream>
#include<string.h>
#include<vector>
using namespace std;
int gra[30][30],n;
vector<int>ls;
int vis[30],mark[30];
void dfs(int s)
{
vis[s]++;
if(vis[s]>=2)return ;
for(int i=0;i<n;i++)
if(gra[s][i])
dfs(i);
}
int main()
{
int m,num;
while(cin>>n>>m,n+m)
{
num=n;
memset(gra,0,sizeof(gra));
memset(mark,0,sizeof(mark));
char str[10];
int flag=0;
for(int i=1;i<=m;i++)
{
cin>>str;
if(flag)continue;
int one=str[0]-'A',two=str[2]-'A';
if(mark[two]==0)num--;
mark[two]++;
gra[one][two]=1;
memset(vis,0,sizeof(vis));
dfs(one);
if(vis[one]>1)
{
flag=1;
cout<<"Inconsistency found after "<<i<<" relations."<<endl;
}
if(num!=1)continue;
int temp[30];
memcpy(temp,mark,sizeof(mark));
ls.clear();
for(int j=1;j<=n;j++)
{
int k=-1;
for(int l=0;l<n;l++)
if(temp[l]==0)
{
k=l;break;
}
if(k==-1)break;
ls.push_back(k);
temp[k]=-1;
for(int l=0;l<n;l++)
if(gra[k][l])
temp[l]--;
}
int gu=0;
for(int j=0;j<n-1;j++)
{
memset(vis,0,sizeof(vis));
dfs(ls[j]);
if(vis[ls[j+1]]==0){gu=1;break;}
}
if(ls.size()==n&&gu==0)
{
flag=1;
cout<<"Sorted sequence determined after "<<i<<" relations: ";
for(int j=0;j<n;j++)
cout<<(char)(ls[j]+'A');
cout<<"."<<endl;
}
}
if(flag==0)
cout<<"Sorted sequence cannot be determined."<<endl;
}
}