poj2240 Arbitrage (spfa判环)

Description

Input

Output

Sample Input

3
USDollar
BritishPound
FrenchFranc
3
USDollar 0.5 BritishPound
BritishPound 10.0 FrenchFranc
FrenchFranc 0.21 USDollar

3
USDollar
BritishPound
FrenchFranc
6
USDollar 0.5 BritishPound
USDollar 4.9 FrenchFranc
BritishPound 10.0 FrenchFranc
BritishPound 1.99 USDollar
FrenchFranc 0.09 BritishPound
FrenchFranc 0.19 USDollar

0

Sample Output

Case 1: Yes
Case 2: No

Source

#include <stdio.h>
#include <vector>
#include <string.h>
#include <queue>
using namespace std;
int n,m;
//邻接表 
vector<int>map[33];
//存贮国家名字 
char name[33][100];
//两个国家的汇率 
double f[33][33];
//起点国家到当前国家转换后的货币量 
double price[33];
//入度 
int in_degree[33];
//进队列的次数 
int sum[33];
//是否在队列 
bool in_queue[33];
int tonum(char *str)
{
	for(int i=0;i<n;i++)
	if(strcmp(str,name[i])==0)
	return i;
}
bool spfa(int x)
{
	queue<int>s;
	sum[x]++;
	price[x]=1.0;
	in_queue[x]=true;
	s.push(x);
	while(!s.empty())
	{
		int pos=s.front();
		s.pop();
		in_queue[pos]=false;
		for(int i=0;i<map[pos].size();i++)
		{
			int edge=map[pos][i];
			if(price[edge]<price[pos]*f[pos][edge])
			{
				price[edge]=price[pos]*f[pos][edge];
				if(!in_queue[edge])
				{
					in_queue[edge]=true;
					s.push(edge);
					if(++sum[edge]>in_degree[edge])
					{
						return true;
					}
				}
			}
		}
	}
	return false;
	
}
int main()
{
	int t=0;
	while(~scanf("%d",&n))
	{
		if(n==0)
		break;
		memset(in_degree,0,sizeof(in_degree));
		memset(name,0,sizeof(name));
		memset(map,0,sizeof(map));
		memset(f,0,sizeof(f));
		for(int i=0;i<n;i++)
		scanf("%s",name[i]);
		scanf("%d",&m);
		for(int i=0;i<m;i++)
		{
			char str1[100],str2[100];
			memset(str1,0,sizeof(str1));
			memset(str2,0,sizeof(str2));
			double x;
			scanf("%s %lf %s",str1,&x,str2);
			int a=tonum(str1);
			int b=tonum(str2);
			f[a][b]=x;
			in_degree[b]++;
			map[a].push_back(b);
		}
		bool ok=false;
		for(int i=0;i<n;i++)
		{
			if(spfa(i))
			{
				ok=true;
				break;
			}
			memset(in_queue,false,sizeof(in_queue));
			memset(price,0,sizeof(price));
			memset(sum,0,sizeof(sum));
		}
		if(ok)
		printf("Case %d: Yes\n",++t);
		else
		printf("Case %d: No\n",++t);
	}
	return 0; 
}