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

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdlib>
 4 #include <cstdio>
 5 #include <cmath>
 6 #include <cctype>
 7 #include <algorithm>
 8 #include <numeric>
 9 
10 #define typec int
11 using namespace std;
12 
13 const int V = 1005;
14 const typec inf = 0xffff;
15 int vis[V];
16 typec lowc[V];
17 int Map[V][V];
18 
19 typec prim (typec cost[][V], int n) {
20     int i, j, p;
21     typec minc, res = 0;
22     memset(vis, 0, sizeof(vis));
23     vis[0] = 1;
24     for (i = 1; i < n; ++ i) lowc[i] = cost[0][i];
25     for (i = 1; i < n; ++ i) {
26         minc = inf; p = -1;
27         for (j = 0 ; j < n; ++ j) {
28             if (0 == vis[j] && minc > lowc[j]) {
29                 minc = lowc[j]; p = j;
30             }
31         }
32         if (inf == minc) return -1;
33         res += minc; vis[p] = 1;
34         for (j = 0 ; j < n; ++ j) {
35             if (0 == vis[j] && lowc[j] > cost[p][j]) {
36                 lowc[j] = cost[p][j];
37             }
38         }
39     }
40     return res;
41 }
42 
43 int main () {
44     int n, road_n;
45     int cur = 0;
46     while (cin >> n >> road_n) {
47         /*if (cur ++ != 0) {
48             cout << endl;
49         }*/
50         for (int i = 0 ; i < n; ++ i) {
51             for (int j = 0 ; j < n; ++ j) {
52                 if (i == j) Map[i][j] = 0;
53                 else {
54                     Map[i][j] = inf;
55                 }
56             }
57         }
58 
59         for (int i = 0 ; i < road_n; ++ i) {
60             int x, y, c;
61             scanf("%d%d%d", &x, &y, &c);
62             if (x == y) {
63                 continue;
64             }
65             Map[x][y] = Map[y][x] = min(Map[x][y], c);
66         }
67 
68         int ans = prim (Map, n);
69 
70         if (ans == -1) {
71             cout << "impossible" << endl << endl;
72         } else {
73             cout << ans << endl << endl;
74         }
75     }
76     return 0;
77 }