【map && spfa求正权回路】HDU - 1217 Arbitrage

Problem Description

给你n种货币，给你m种货币与货币兑换的比例。让你寻找存不存在一种兑换方式使得自己的钱变多。

思路：因为都是货币种类都是字符串，所以用map映射成整数这样会好求很多

#include<cstdio>
#include<queue>
#include<map>
#include<cstring>
#include<string>
#include<iostream>
using namespace std;
struct node
{
    int to; double w; int next;
};
node e[1000];
int head[1000], n;
int Spfa()
{
    int vis[35], out[35];
    double dist[35];
    memset(dist, 0, sizeof(dist));//正权回路所以初始化0
    memset(out, 0, sizeof(out));
    memset(vis, 0, sizeof(vis));
    dist[1] = 1; vis[1] = 0;
    queue<int> q; q.push(1);
    while(!q.empty())
    {
        int u = q.front(); q.pop();
        vis[u] = 0;
        for(int i = head[u]; ~i; i = e[i].next)
        {
            int x = e[i].to; double y = e[i].w;
            if(dist[x] < dist[u] * y)
            {
                out[x]++;
                if(out[x] > n) return 0;//一个点松弛超过n次代表有正权回路
                dist[x] = dist[u] * y;
                if(!vis[x])
                {
                    vis[x] = 1;
                    q.push(x);
                }
            }
        }
    }
    return 1;
}
int main()
{
    int m, cas = 1;
    while(~scanf("%d", &n) && n)
    {
        string s, str;
        map<string, int> Ys;
        memset(head, -1, sizeof(head));
        for(int i = 1; i <= n; i++)
        {
            cin >> s;
            Ys[s] = i;//映射成整数
        }
        scanf("%d", &m);
        double num;
        int cnt = 0;
        while(m--)
        {
            cin >> s >> num >> str;
            e[cnt].to = Ys[str];//前向星存图
            e[cnt].w = num;
            e[cnt].next = head[Ys[s]];
            head[Ys[s]] = cnt++;
        }
        printf("Case %d: ", cas++);
        if(!Spfa()) printf("Yes\n");
        else printf("No\n");
    }
    return 0;
}