POJ-1094-Sorting It All Out（拓扑排序）

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Sorting It All Out

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 32037 Accepted: 11131

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

注意：判断    1，构成环   2，有序  3，无序。

     1,2成立立刻无视后续数据输出。

//#include <bits/stdc++.h>#include <cstring>#include <iostream>#include <algorithm>#include <cstdio>using namespace std;int Scan(){    int res=0,ch,flag=0;    if((ch=getchar())=='-')flag=1;    else if(ch>='0'&&ch<='9')res=ch-'0';    while((ch=getchar())>='0'&&ch<='9')res=res*10+ch-'0';    return flag?-res:res;}void Out(int a){if(a>9)Out(a/10);putchar(a%10+'0');}int n,m;char str[5];int map_[30][30],in[30],p[30],stack_[30];int TopoSort(){    memcpy(p,in,sizeof(in));    int top=0,flag=1;    for(int i=1; i<=n; ++i)    {        int temp=0,poi;        for(int j=1; j<=n; ++j)        if(p[j]==0){temp++; poi=j;}        if(!temp)return 0;//构成环        if(temp>1)flag=-1;//无序        stack_[top++]=poi;        p[poi]=-1;        for(int j=1; j<=n; ++j)            if(map_[poi][j])p[j]--;    }    return flag;//有序}int main(){    while(scanf("%d%d",&n,&m)!=EOF)    {        if(!n||!m)break;        memset(in,0,sizeof(in));        memset(map_,0,sizeof(map_));        int flag=0;        for(int i=1; i<=m; ++i)        {            scanf("%s",str);            if(flag)continue;            int a=str[0]-'A'+1;            int b=str[2]-'A'+1;            map_[a][b]=1;            ++in[b];            int poi=TopoSort();            if(poi==0)            {                printf("Inconsistency found after %d relations.\n",i);                flag=1;            }            else if(poi==1)            {                printf("Sorted sequence determined after %d relations: ",i);                for(int j=0;j<n;j++)                    printf("%c",stack_[j]+'A'-1);                printf(".\n");                flag=1;            }        }        if(!flag)printf("Sorted sequence cannot be determined.\n");    }    return 0;}