poj2240 Arbitrage

思路：

有向图判负环。

实现：

（1）spfa

#include <iostream>
#include <map>
#include <string>
#include <cmath>
#include <queue>
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAXN = 35;
double G[MAXN][MAXN], d[MAXN];
bool in[MAXN];
int n, m, num[MAXN];
bool spfa(int s)
{
    queue<int> q;
    d[s] = 0;
    q.push(s);
    in[s] = true;
    while (!q.empty())
    {
        int tmp = q.front(); q.pop();
        in[tmp] = false;
        for (int i = 0; i <= n; i++)
        {
            if (d[tmp] + G[tmp][i] < d[i])
            {
                d[i] = d[tmp] + G[tmp][i];
                if (!in[i]) { in[i] = true; q.push(i); }
                num[i]++;
                if (num[i] > n) return true;
            }
        }
    }
    return false;
}
int main()
{
    map<string, int> mp;
    string s, t;
    double x;
    int Kase = 1;
    while (cin >> n, n)
    {
        for (int i = 0; i <= n; i++)
        {
            for (int j = 0; j <= n; j++)
            {
                G[i][j] = INF;
            }
        }
        fill(d, d + n + 1, INF);
        fill(in, in + n + 1, 0);
        fill(num, num + n + 1, 0);
        mp.clear();
        for (int i = 1; i <= n; i++)
        {
            cin >> s;
            mp[s] = i;
        }
        cin >> m;
        for (int i = 1; i <= m; i++)
        {
            cin >> s >> x >> t;
            G[mp[s]][mp[t]] = -log(x);
        }
        for (int i = 1; i <= n; i++) G[0][i] = 0;
        cout << "Case " << Kase++ << ": ";
        if (spfa(0)) cout << "Yes" << endl;
        else cout << "No" << endl;
    }
    return 0;
}

（2）floyd

#include <iostream>
#include <map>
#include <string>
#include <cmath>
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAXN = 35;
double G[MAXN][MAXN];
int n, m;

int main()
{
    map<string, int> mp;
    string s, t;
    double x;
    int Kase = 1;
    while (cin >> n, n)
    {
        for (int i = 1; i <= n; i++)
        {
            for (int j = 1; j <= n; j++)
            {
                if (i == j) G[i][j] = 0;
                else G[i][j] = INF;
            }
        }
        mp.clear();
        for (int i = 1; i <= n; i++)
        {
            cin >> s;
            mp[s] = i;
        }
        cin >> m;
        for (int i = 1; i <= m; i++)
        {
            cin >> s >> x >> t;
            G[mp[s]][mp[t]] = -log(x);
        }
        for (int k = 1; k <= n; k++)
        {
            for (int i = 1; i <= n; i++)
            {
                for (int j = 1; j <= n; j++)
                {
                    if (G[i][k] + G[k][j] < G[i][j])
                        G[i][j] = G[i][k] + G[k][j];
                }
            }
        }
        bool flg = false;
        for (int i = 1; i <= n; i++)
        {
            if (G[i][i] < 0) { flg = true; break; }
        }
        cout << "Case " << Kase++ << ": ";
        if (flg) cout << "Yes" << endl;
        else cout << "No" << endl;
    }
    return 0;
}