find the safest road---hdu1596(最短路模板求最大概率)

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1596

求给定的任意两点之间的最大安全概率，概率之间是相乘的关系，所以注意初始化即可

#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<math.h>
#include<string.h>
#include<string>
#include<stack>
#include<vector>
#include<map>
using namespace std;
#define N 1210
#define INF 0x3f3f3f3f
#define met(a, b) memset(a, b, sizeof(a))
typedef long long LL;

double dist[N], G[N][N];
int vis[N], n;

double Dijkstra(int s, int e)
{
    for(int i=1; i<=n; i++)
        dist[i] = 0;
    for(int i=1; i<=n; i++)
        dist[i] = G[s][i];
    met(vis, 0);
    vis[s] = 1;
    for(int i=1; i<=n; i++)
    {
        double Max = -INF;
        int Index = -1;
        for(int j=1; j<=n; j++)
        {
            if(dist[j]>Max && !vis[j])
            {
                Max = dist[j];
                Index = j;
            }
        }
        if(Index == -1)break;
        vis[Index] = 1;
        for(int j=1; j<=n; j++)
        {
            if(!vis[j] && dist[j] < dist[Index]*G[Index][j])
                dist[j] = dist[Index]*G[Index][j];
        }
    }
    return dist[e];
}

int main()
{
    int m;
    while(scanf("%d", &n)!=EOF)
    {
        for(int i=1; i<=n; i++)
        {
            for(int j=1; j<=n; j++)
                scanf("%lf", &G[i][j]);
        }
        scanf("%d", &m);
        for(int i=1; i<=m; i++)
        {
            int u, v;
            scanf("%d %d", &u, &v);
            double ans = Dijkstra(u, v);

            if(ans == 0)
                puts("What a pity!");
            else
                printf("%.3lf
", ans);
        }
    }
    return 0;
}