[POJ](1094)Sorting It All Out ---拓扑排序（图）

Sorting It All Out

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 35706 Accepted: 12565

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

解题新知：(*@ο@*) 哇～这道题看了好长时间，理解题意是关键，还要注意题意情况的优先级关系。/(ㄒoㄒ)/~~不说了，还是看前辈们的思路和做法吧。自己也是稍微理解，稍微改了改前辈的代码。

参考：http://www.cnblogs.com/pushing-my-way/archive/2012/08/23/2652033.html

AC代码：

#include<iostream>#include<cstring>#include<cstdio>#include<algorithm>#include<queue>using namespace std;int mmap[30][30];int indegree[30];//int copyindegree[30];int llist[30];int n,m;int topoSort(){    queue<int>q;    int copyindegree[30];    for(int i=0;i<n;i++)    {        copyindegree[i]=indegree[i];        if(!indegree[i])            q.push(i);    }    int flag=0;    int num=0;    int k=-1;    while(!q.empty())    {        if(q.size()>1)            flag=1;        k=q.front();        q.pop();        llist[num++]=k;        for(int i=0;i<n;i++)        {            if(mmap[k][i]==1)            {                copyindegree[i]--;                if(copyindegree[i]==0)                    q.push(i);            }        }    }    if(num!=n)        return 1;    else if(flag)        return 2;    return 0;}int main(){    while(cin>>n>>m && n && m)    {        int determined=0;//唯一升序序列确定        int inconsistency=0;//矛盾        char s[5];        int u,v;        int res;        memset(mmap,0,sizeof(mmap));        memset(indegree,0,sizeof(indegree));        memset(llist,0,sizeof(llist));        for(int i=1;i<=m;i++)        {            cin>>s;            u=s[0]-'A';            v=s[2]-'A';            if(!determined && !inconsistency)            {                if(mmap[v][u]==1)                {                    inconsistency=1;                    printf("Inconsistency found after %d relations.\n",i);                    continue;//???                }                if(mmap[u][v]==0)                {                    mmap[u][v]=1;                    indegree[v]++;                }                res=topoSort();                if(res==0)                {                    printf("Sorted sequence determined after %d relations: ",i);                    for(int j=0;j<n;j++)                        printf("%c",llist[j]+'A');                    printf(".\n");                    determined=1;                }                else if(res==1)                {                    printf("Inconsistency found after %d relations.\n",i);                    inconsistency=1;                }            }        }        if(!determined && !inconsistency)        {            printf("Sorted sequence cannot be determined.\n");        }    }    return 0;}