Billman_ford货币升值——正权回路

2240和1860那个题目很像啊

都是问货币能不能增多，钻社会制度得空子啊哈哈

唯一不同得是你的起点是任意一个点，这个比较麻烦了，多了一层循环嘞

处理货币名可以用map分配id

然后就是老套的Billman_ford算法了

#include <iostream>
#include <map>
#include <vector>
#include <string.h>
#include <cstdio>
#include <string>
using namespace std;
const int maxn = 40;
map<string,int> id;
double dis[maxn];
struct node{
    int from,to;
    double v;
    node(int f,int t,double va):from(f),to(t),v(va){}
    node(){}
};

这次联系了Stl中得容器，熟悉熟悉

int main()
{
    int n,m;
    string s,a,b;
    double v;
    int cas = 1;
    while(~scanf("%d",&n),n)
    {
        id.clear();
        edge.clear();
        for(int i = 1;i <= n;i++)
        {
            cin>>s;
            id[s] = i;
        }
        scanf("%d",&m);
        while(m--)
        {
            cin>>a;
            scanf("%lf",&v);
            cin>>b;
            edge.push_back(node(id[a],id[b],v));
        }
        printf("Case %d: ",cas++);
        for(int i = 1;i <= n;i++)
        {
            if(blm(i,n))
            {
                printf("Yes\n");
                break;
            }
            else if(i == n)printf("No\n");
        }
    }
    return 0;
}

vector<node> edge;
bool blm(int s,int n)
{
    for(int i = 1;i <= n;i++)dis[i] = 0;
    dis[s] = 1.0;
    for(int i = 1;i < n;i++)
    {
        for(int j = 0;j < edge.size();j++)
        {
            int from = edge[j].from;
            int to = edge[j].to;
            double v = edge[j].v;
            //cout<<from<<" "<<to<<" "<<v<<endl;
            dis[to] = max(dis[to],dis[from] * v);
        }
        //cout<<"cs"<<endl;
    }
    for(int i = 0;i < edge.size();i++)
    {
        int from = edge[i].from;
        int to = edge[i].to;
        double v = edge[i].v;
        if(dis[to] < dis[from] * v)return true;
    }
    return false;
}