HDU 1217 Arbitrage（最短路径，Floyd算法，map函数）

Problem Description

Arbitrage is the use of discrepancies in currency exchange rates to transform one unit of a currency into more than one unit of the same currency. For example, suppose that 1 US Dollar buys 0.5 British pound, 1 British pound buys 10.0 French francs, and 1 French franc buys 0.21 US dollar. Then, by converting currencies, a clever trader can start with 1 US dollar and buy 0.5 * 10.0 * 0.21 = 1.05 US dollars, making a profit of 5 percent.

Your job is to write a program that takes a list of currency exchange rates as input and then determines whether arbitrage is possible or not.

 

Input

The input file will contain one or more test cases. Om the first line of each test case there is an integer n (1<=n<=30), representing the number of different currencies. The next n lines each contain the name of one currency. Within a name no spaces will appear. The next line contains one integer m, representing the length of the table to follow. The last m lines each contain the name ci of a source currency, a real number rij which represents the exchange rate from ci to cj and a name cj of the destination currency. Exchanges which do not appear in the table are impossible.
Test cases are separated from each other by a blank line. Input is terminated by a value of zero (0) for n.

 

Output

For each test case, print one line telling whether arbitrage is possible or not in the format "Case case: Yes" respectively "Case case: No".

 

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

 

最短路径，弗洛伊德算法，dp，用到了map函数

#include<stdio.h>
#include<string>
#include<iostream>
#include<map>
using namespace std;
const int INF=0.00001;
int n,m,t;
double dp[50][50],c;
string s[50],x1,x2;
map<string,int>p;

int main(){
    t=1;
    while(scanf("%d",&n)!=EOF&&n){
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
                dp[i][j]=INF; //初始化
        for(int i=1;i<=n;i++){
            cin>>s[i];
            p[s[i]]=i;
        }
    /*    map<string,int>::iterator iter;  //map函数的用法 
        for(iter=p.begin();iter!=p.end();iter++)
         cout<<iter->first<<"   "<<iter->second<<endl;*/
        cin>>m;
        for(int i=1;i<=m;i++){
            cin>>x1>>c>>x2;
            dp[p[x1]][p[x2]]=c;
        }
        for(int i=1;i<=n;i++)//floyd算法 
            for(int j=1;j<=n;j++)    
                for(int k=1;k<=n;k++)
                    if(dp[j][i]*dp[i][k]>dp[j][k])
                        dp[j][k]=dp[j][i]*dp[i][k];
        printf("Case %d: ",t++);
        if(dp[1][1]>1)//因为是自己到自己的转换，所以dp[1][1]，如果自己到终点的转换，dp[1][n] 
            printf("Yes
");
        else
             printf("No
");
    }
}