HDU 1227 Arbitrage（spfa)

Arbitrage

#include <stdio.h>
#include <iostream>
#include <cstring>
#include <map>
#include <queue>
#include <algorithm>
using namespace std;

const int L = 35;
const double inf = 1000000;
map<string,int> mat;
int n,m;
char str[105], s1[105], s2[105];
double trip[35][35], dis[35];

int SPFA(int src) {
    queue<int> Q;
    int vis[35],i;
    int num[35];

    for(i = 1; i <= n; i++)
        vis[i] = dis[i] = num[i] = 0;

    while(!Q.empty())
        Q.pop();

    dis[src] = 1.0;
    vis[src] = 1;
    Q.push(src);

    while(!Q.empty()) {
        int now = Q.front();
        Q.pop();
        vis[now] = 0;
        for(i = 1; i <= n; i++) {
            if(dis[now]*trip[now][i] > dis[i]) {
                dis[i] = dis[now]*trip[now][i];

                if(dis[src]>1.0)
                    return 1;
                if(!vis[i]) {
                    vis[i] = 1;
                    Q.push(i);
                }
            }
        }
    }

    return 0;
}

int main() {
    freopen("data.in", "r", stdin);
    int i, j, cas = 1;
    double w;
    while(~scanf("%d", &n), n) {
        mat.clear();
        for(i = 1; i <= n; i++)
            for(j = 1; j <= n; j++)
                trip[i][j] = (i==j)?1.0:0;

        for(i = 1; i <= n; i++) {
            scanf("%s",str);
            mat[str] = i;
        }

        scanf("%d", &m);
        while(m--) {
            scanf("%s%lf%s", s1, &w, s2);
            trip[mat[s1]][mat[s2]] = w;
        }

        int flag = 0;
        for(i = 1; i <= n; i++) {
            if(SPFA(i)) {
                flag = 1;
                break;
            }
        }

        printf("Case %d: %s\n",cas++, flag ? "Yes" : "No");
    }

    return 0;
}