UVa 1395 苗条的生成树（Kruskal+并查集）

 1 #include<iostream> 
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5 
 6 const int maxn = 100 + 5;
 7 
 8 int n, m, ans;
 9 int p[maxn];
10 
11 struct node
12 {
13     int u;
14     int v;
15     int w;
16 }edge[maxn*maxn];
17 
18 int find(int x)
19 {
20     return p[x] == x ? x : find(p[x]);
21 }
22 
23 bool cmp(node a, node b)
24 {
25     return a.w < b.w;
26 }
27 
28 
29 void init()
30 {
31     for (int k = 1; k <= n; k++)   p[k] = k;
32 }
33 
34 void Kruskal()
35 {
36     int ok = 0;
37     sort(edge, edge + m, cmp);
38     for (int i = 0; i <= m - n + 1; i++)
39     {
40         int num = 0;
41         init();
42         for (int j = i ; j < m; j++)
43         {
44             int x = find(edge[j].u);
45             int y = find(edge[j].v);
46             if (x != y)
47             {
48                 p[x] = y;
49                 num++;
50             }
51             if (num == n - 1)
52             {
53                 ans = min(ans, edge[j].w - edge[i].w);
54                 ok = 1;
55                 break;
56             }
57         }
58         while (edge[i].w == edge[i + 1].w)   i++;
59     }
60     if (!ok)    printf("-1\n");
61     else         printf("%d\n", ans);
62 }
63 
64 int main()
65 {
66     //freopen("D:\\txt.txt", "r", stdin);
67     while (scanf("%d%d",&n,&m))
68     {
69         if (n == 0 && m == 0)    break;
70         for (int i = 0; i<m ; i++)
71         {
72             scanf("%d%d%d", &edge[i].u, &edge[i].v , &edge[i].w);
73         }
74         ans = 1000000000;
75         Kruskal();
76     }
77     return 0;
78 }
79