[POJ] 1094 Sorting It All Out

Sorting It All Out
Time Limit: 1000MS      Memory Limit: 10000K
Total Submissions: 37417        Accepted: 13220
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.
Source

East Central North America 2001

最失败的题之一，调了太久，很难受。

topo()的返回值写成bool，查良久，无果。。

本质就是拓扑排序，把字母当成节点，建图，不过加入了几个特殊的条件，有环或者无法完全排序都是特殊情况，要特殊判断，但是判断完了剩下的数据仍然得输入。

然后输出的部分，句号什么的，很难受。写的时候也是很混乱..

可能今天心情不好…

//Stay foolish,stay hungry,stay young,stay simple
#include<iostream>
#include<queue>
#include<cstdio>
#include<cstring>
using namespace std;

const int MAXN=20000;

int n,m;

struct Edge{
    int next,to;
}e[MAXN];
int ecnt,head[MAXN],ind[MAXN];
inline void add(int x,int y){
    e[++ecnt].next = head[x];
    e[ecnt].to = y;
    head[x] = ecnt;
}
int tmp[MAXN];
int ans[MAXN],anscnt;
int topo(){
    anscnt=0;
    memcpy(tmp,ind,sizeof(ind));
    int ret=1;
    for(int i=1;i<=n;i++){
        int cnt=0,pos;
        for(int j=1;j<=n;j++)
            if(tmp[j]==0) cnt++,pos=j;
        if(cnt==0) return 0;//circle
        if(cnt>1) ret=-1;//unsure 
        tmp[pos]=-1;//
        ans[++anscnt]=pos;
        for(int j=head[pos];j;j=e[j].next){
            int v=e[j].to;
            tmp[v]--;
        }
    }
    return ret;
}



void slove(){
    bool succ=0;
    for(int i=1;i<=m;i++){
        char s[5];
        cin>>s;
        if(succ) continue;
        int x=s[0]-'A'+1;
        int y=s[2]-'A'+1;
        add(x,y);
        ind[y]++;

        int res=topo();

        if(res==0){
            printf("Inconsistency found after %d relations.
",i);
            succ=1;
        }
        if(res==1){
            printf("Sorted sequence determined after %d relations: ",i);
            for(int j=1;j<=anscnt;j++) cout<<char(ans[j]+'A'-1);
            printf(".
");
            succ=1;//
        }
    }
    if(!succ) printf("Sorted sequence cannot be determined.
");
}

int main(){
//  freopen("test.txt","r",stdin);
    while(cin>>n>>m&&n){
        ecnt=0,anscnt=0;
        memset(head,0,sizeof(head));
        memset(ind,0,sizeof(ind));
        slove();
    }
    return 0;
}