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

——written by Lyon