POJ 1094 Sorting It All Out(拓扑排序)

Sorting It All Out

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 30159 Accepted: 10430

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.

每次输入都要进行一次拓扑排序，有环直接输出Inconsistency found after i relations.（i为输入的次数）

如果排序完成 输出在第几次结束 并输出这个排序结果

两者都没有 最后输出   Sorted sequence cannot be determined.

#include <iostream>#include <stdlib.h>#include <cstdio>#include <cstring>#include <algorithm>#define N 30using namespace std;int a[N][N],v[N],ans[N];int n,m;int Solve(){    int ss=1;    int b[N];    for(int i=0;i<n;i++)     b[i]=v[i];    for(int i=0; i<n; i++)    {        int sum=0;        for(int j=0;j<n;j++)        {            if(b[j]==0)                sum++;        }        if(sum==0) ss=0;         //没有入度为0的点 说明有环        if(sum>1)  ss=-1;        //入度为0的点不止一个 无法判定顺序        for(int j=0; j<n; j++)        {            if(b[j]==0)            {                ans[i]=j;                b[j]--;                for(int k=0; k<n; k++)                {                    if(a[j][k])                    {                        b[k]--;                    }                }                break;            }        }    }    return ss;}int main(){    while(scanf("%d%d",&n,&m) && (m ||n))    {        memset(a,0,sizeof(a));        memset(v,0,sizeof(v));        bool flag = true;        for(int i=1; i<=m; i++)        {            char x,y,z;            cin>>x>>z>>y;            if(a[x-'A'][y-'A']==0)            {                a[x-'A'][y-'A']=1;                v[y-'A']++;            }            if(flag)            {                int ss=Solve();                if(ss==0)                {                    flag=false;                    printf("Inconsistency found after %d relations.\n",i);                }                if(ss==1)                {                    flag=false;                    printf("Sorted sequence determined after %d relations: ",i);                    for(int j=0; j<n-1; j++)                        printf("%C",ans[j]+'A');                    printf("%C.\n",ans[n-1]+'A');                }            }        }        if(flag)            printf("Sorted sequence cannot be determined.\n");    }    return 0;}