HDU - 1596 find the safest road （最短路水题）

[code]#include <cstdio>
#include <cstring>
#include <cmath>
#include <queue>
#define INF 0x3f3f3f3f
#define N 1010
#define M 1000010
#define esp 1e-8
using namespace std;
struct Node {
    int to, next;
    double len;
}node[M];

int n, m, cnt, s, e, head
;
bool vis
;
double d
, dis

;

void init() {

    double x;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++) {
            scanf("%lf", &dis[i][j]);
        }
}

bool dij() {
    bool flag = false;;
    for (int i = 1; i <= n; i++) {
        d[i] = 0.0;
        vis[i] = false;
    }

    d[s] = 1.0;
    for (int i = 1; i <= n - 1; i++) {
        int x;
        double tmp = 0.0;
        for (int j = 1; j <= n; j++) {
            if (!vis[j] && d[j] - tmp > esp) {
                tmp = d[j];
                x = j;
            }
        }
        if (x == e)
            return true;
        vis[x] = true;
        for (int j = 1; j <= n; j++) {
            if (!vis[j] && d[x] * dis[x][j] - d[j] > esp) {
                d[j] = d[x] * dis[x][j];
                if (j == e)
                    flag = true;
            }
        }
    }
    return flag;
} 

void solve() {
    scanf("%d", &m);
    int x, y;
    for (int i = 0; i < m; i++) {
        scanf("%d%d", &s, &e);
        if (!dij())
            printf("What a pity!\n");
        else
            printf("%.3lf\n", d[e]);
    }
}

int main() {
    while (scanf("%d", &n) != EOF) {
        init();
        solve();
    }
    return 0;
}