POJ 1094 Sorting It All Out 拓扑排序

Sorting It All Out

Time Limit:1000MS     Memory Limit:10000KB     64bit IO Format:%lld & %llu

 

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.



套模板硬上

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <vector>
#include <iomanip>
#include <math.h>
#include <map>
using namespace std;
#define FIN     freopen("input.txt","r",stdin);
#define FOUT    freopen("output.txt","w",stdout);
#define INF     0x3f3f3f3f
#define lson    l,m,rt<<1
#define rson    m+1,r,rt<<1|1
typedef long long LL;

const int MAXN=1e5+5;

struct Edge{
   int v,nxt;
}E[MAXN*2];

int Head[MAXN],erear;
int IN[MAXN],P[MAXN],sz;
int temp[MAXN];
int n,m,sum;
int flag,ed;
bool con;

void edge_init(){
   erear=0;
   memset(Head,-1,sizeof(Head));
   memset(IN,0,sizeof(IN));
   sum=0;
   con=0;
}

void edge_add(int u,int v){
   E[erear].v=v;
   E[erear].nxt=Head[u];
   Head[u]=erear++;

}

int topsort(){
        sz=0;
        queue<int>Q;
        for(int i=0;i<n;i++){
            if(!IN[i])  Q.push(i);
        }


        bool sign=0;
        while(!Q.empty()){
            if(Q.size()>=2)  sign=1;
            int u=Q.front();
            Q.pop();
            P[sz++]=u;
            for(int i=Head[u];~i;i=E[i].nxt){
                int v=E[i].v;
                IN[v]--;
                if(!IN[v])  Q.push(v);
            }
        }

        if(sz<n){
            //printf("invalid
");
            return 1;
        }else if(sign){
            //printf("multi ans
");
            return 2;
        }else{
            return 3;
        }
        /*for(int i=0;i<sz;i++){
            if(i==0)  printf("%d",P[i]);
            else  printf(" %d",P[i]);
        }
        printf("
");*/

}


int main()
{
    //FIN
    while(~scanf("%d%d",&n,&m))
    {
        if(n==0&&m==0)  break;
        edge_init();
        flag=2;
        char op[10];
        for(int i=1;i<=m;i++){
            scanf("%s",op);
            if(con)  continue;
            int u=(int)op[0]-'A';
            int v=(int)op[2]-'A';
            if(op[1]=='>'){
                edge_add(u,v);
                IN[v]++;
            }
            else{
                edge_add(v,u);
                IN[u]++;
            }
            memcpy(temp,IN,sizeof(IN));
            flag=topsort();
            memcpy(IN,temp,sizeof(temp));
            sum=i;
            if(flag!=2){
                ed=i;
                con=true;
            }
        }


            if(flag==3){
                printf("Sorted sequence determined after %d relations: ", ed);
                for(int i=sz-1; i>=0; --i)
                   printf("%c",P[i]+'A');
                   printf(".
");
            }
            else if(flag==1){
                printf("Inconsistency found after %d relations.
",ed);
            }
            else{
                printf("Sorted sequence cannot be determined.
");
            }


    }
    return 0;
}