Hoj 1336/Poj 1094 Sorting It All Out

题目：http://acm.hit.edu.cn/hoj/problem/view?id=1336
http://poj.org/problem?id=1094
本题联系拓扑排序。

如果给定的所有偏序关系中，能求得唯一的拓扑排序，则输出：Sorted sequence determined after xxx relations: yyy...y.

如果有环，则输出：Inconsistency found after xxx relations.

如果有不止一个拓扑序，则输出：Sorted sequence cannot be determined.

由于需要记录下在第几个偏序关系中能得出结论，所以每读入一个偏续就需要进行一次排序判断，toposort()可以作为拓扑排序的模板。

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <algorithm>
#include <stack>
#include <queue>
#include <string>
using namespace std;

int map[30][30];
int indegree[30];
int n,m;

queue<int> q;
queue<int> record;

//拓扑排序
int toposort()
{
//清空队列
while(!q.empty())
{
q.pop();
}
while(!record.empty())
{
record.pop();
}
int in[30];
memcpy(in,indegree,sizeof(indegree));
for(int i=0;i<n;i++)
{
if(in[i] == 0)
{
q.push(i);
}
}

int flag = 0;
while(!q.empty())
{
int a = q.front();
record.push(a);
q.pop();
if(!q.empty())
{
flag = 1;
}
for(int i=0;i<n;i++)
{
if(map[a][i] == 1)
{
in[i]--;
if(in[i] == 0)
{
q.push(i);
}
}
}
}
//有环路
if(record.size()!=n)
{
return 0;
}
//不确定排序方式
else if(flag == 1)
{
return 1;
}
return 2;//有唯一拓扑
}

int main()
{
#ifndef ONLINE_JUDGE
freopen("in.txt","r",stdin);
#endif

while(scanf(" %d %d",&n,&m)!=EOF && n!=0 && m!=0)
{
memset(map,0,sizeof(map));
memset(indegree,0,sizeof(indegree));

int flag = 0;
for(int i=0;i<m;i++)
{
char a,b;
scanf(" %c<%c",&a,&b);
if(map[b-'A'][a-'A'] == 1)
{
flag = 1;
printf("Inconsistency found after %d relations.\n",i+1);
for(int j=i+1;j<m;j++)
{
scanf(" %c<%c",&a,&b);
}
break;
}
else if(map[a-'A'][b-'A'] == 0)
{
map[a-'A'][b-'A'] = 1;
indegree[b -'A']++;
}
int res = toposort();
if(res == 0)
{
flag = 1;
printf("Inconsistency found after %d relations.\n",i+1);
for(int j=i+1;j<m;j++)
{
scanf(" %c<%c",&a,&b);
}
break;
}
else if(res == 2)
{
flag = 1;
for(int j=i+1;j<m;j++)
{
scanf(" %c<%c",&a,&b);
}
printf("Sorted sequence determined after %d relations: ",i+1);
while(!record.empty())
{
int top = record.front();
record.pop();
printf("%c",top + 'A');
}
printf(".\n");
break;
}
}
if(flag == 0)
{
printf("Sorted sequence cannot be determined.\n");
}

}
return 0;
}