【HDU2122】Ice_cream’s world III（MST基础题）

2坑，3次WA。

1.判断重边取小。2.自边舍去。

（个人因为vis数组忘记初始化，WA了3次，晕死！！）

 #include <iostream>
 #include <cstring>
 #include <cstdlib>
 #include <cstdio>
 #include <cmath>
 #include <cctype>
 #include <algorithm>
 #include <numeric>

 #define typec int
 using namespace std;

 const int V = ;
 const typec inf = 0xffff;
 int vis[V];
 typec lowc[V];
 int Map[V][V];

 typec prim (typec cost[][V], int n) {
     int i, j, p;
     typec minc, res = ;
     memset(vis, , sizeof(vis));
     vis[] = ;
     for (i = ; i < n; ++ i) lowc[i] = cost[][i];
     for (i = ; i < n; ++ i) {
         minc = inf; p = -;
         for (j =  ; j < n; ++ j) {
             if ( == vis[j] && minc > lowc[j]) {
                 minc = lowc[j]; p = j;
             }
         }
         if (inf == minc) return -;
         res += minc; vis[p] = ;
         for (j =  ; j < n; ++ j) {
             if ( == vis[j] && lowc[j] > cost[p][j]) {
                 lowc[j] = cost[p][j];
             }
         }
     }
     return res;
 }

 int main () {
     int n, road_n;
     int cur = ;
     while (cin >> n >> road_n) {
         /*if (cur ++ != 0) {
             cout << endl;
         }*/
         for (int i =  ; i < n; ++ i) {
             for (int j =  ; j < n; ++ j) {
                 if (i == j) Map[i][j] = ;
                 else {
                     Map[i][j] = inf;
                 }
             }
         }

         for (int i =  ; i < road_n; ++ i) {
             int x, y, c;
             scanf("%d%d%d", &x, &y, &c);
             if (x == y) {
                 continue;
             }
             Map[x][y] = Map[y][x] = min(Map[x][y], c);
         }

         int ans = prim (Map, n);

         if (ans == -) {
             cout << "impossible" << endl << endl;
         } else {
             cout << ans << endl << endl;
         }
     }
     return ;
 }