UVA1395 Slim Span(枚举最小生成树）

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 using namespace std;
 6 const int INF = 0x3f3f3f3f;
 7 const int Max = 5000;
 8 const int N = 110;
 9 int father[N];
10 struct Edge
11 {
12     int x, y, dist;
13 };
14 Edge edge[Max];
15 int cmp(Edge t1, Edge t2)
16 {
17     return t1.dist < t2.dist;
18 }
19 int find_father(int x)
20 {
21     if (x == father[x])
22         return x;
23     return father[x] = find_father(father[x]);
24 }
25 int main()
26 {
27     int n, m;
28     while (scanf("%d%d", &n, &m) != EOF)
29     {
30         if (m == 0 && n == 0)
31             break;
32         for (int i = 0; i < m; i++)
33         {
34             scanf("%d%d%d", &edge[i].x, &edge[i].y, &edge[i].dist);
35         }
36         sort(edge, edge + m, cmp);
37         int minn = INF;
38         for (int i = 0; i < m; i++)
39         {
40             for (int j = 0; j <= n; j++)
41                 father[j] = j;
42             int cnt = 0;
43             for (int j = i; j < m; j++)  // 依次枚举每一个生成树
44             {
45                 int fx = find_father(edge[j].x);
46                 int fy = find_father(edge[j].y);
47                 if (fx != fy)
48                 {
49                     father[fx] = fy;
50                     cnt++;
51                     if (cnt == n - 1) // 一旦构成生成树，j是最大边权，i是最小权，相减更新
52                     {
53                         minn = min(minn, edge[j].dist - edge[i].dist);
54                         break;
55                     }
56                 }
57             }
58         }
59         if (minn == INF)
60             printf("-1\n");
61         else
62             printf("%d\n", minn);
63     }
64     return 0;
65 }