hdu 1596 find the safest road （变形SP && dij+heap）

Problem - 1596

　　变形最短路问题，给出邻接矩阵，要求求出给定点对间安全率最大值。

　　这题可以用dijkstra+heap来做。对于每一个查询，做一次dij即可。

代码如下：

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>

using namespace std;

const int N = 1111;
double wt[N][N];
bool vis[N];
#define _clr(x) memset(x, 0, sizeof(x))
typedef pair<double, int> PDBI;
priority_queue<PDBI> priq;

double dij(int s, int t, int n) {
    while (!priq.empty()) priq.pop();
    _clr(vis);
    for (int i = 0; i < n; i++) priq.push(PDBI(wt[s][i], i));
    while (!priq.empty()) {
        double w = priq.top().first;
        int id = priq.top().second;
        priq.pop();
        if (vis[id]) continue;
//        cout << "id!!! " << id << endl;
        vis[id] = true;
        if (id == t) return w;
        for (int i = 0; i < n; i++) {
            if (vis[i]) continue;
            if (wt[s][i] < wt[s][id] * wt[id][i]) {
                wt[s][i] = wt[s][id] * wt[id][i];
                priq.push(PDBI(wt[s][i], i));
            }
        }
    }
    return wt[s][t];
}

int main() {
//    freopen("in", "r", stdin);
    int n, m;
    while (~scanf("%d", &n)) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                scanf("%lf", &wt[i][j]);
            }
        }
        scanf("%d", &m);
        for (int i = 0, x, y; i < m; i++) {
            scanf("%d%d", &x, &y);
            double ans = dij(x - 1, y - 1, n);
            if (ans < 1e-100) puts("What a pity!");
            else printf("%.3f
", ans);
        }
    }
    return 0;
}

——written by Lyon