POJ 3522 Slim Span

题意：

         求最大边与最小边差值最小的生成树，若不存在生成树则输出-1。

思路：

         用Kruskal算法枚举最小边即可

 1 #include <cstdio>
 2 #include <algorithm>
 3 using namespace std;
 4 const int N = 110, M = 5000;
 5 struct SIDE
 6 {
 7     int from;
 8     int to;
 9     int distance;
10 }edge[M];
11 int cnt[N];
12 bool cmp(const SIDE a, const SIDE b){
13     return a.distance < b.distance;
14 }
15 int Find(int x){
16     return cnt[x] == x ? x : Find(cnt[x]);
17 }
18 int main(void)
19 {
20     int n, m, a, b, MIN, ok;
21     while(scanf("%d %d", &n, &m), n+m)
22     {
23         for(int i=0; i<m; ++i)
24             scanf("%d %d %d", &edge[i].from, &edge[i].to, &edge[i].distance);
25         sort(edge, edge+m, cmp);
26         MIN = 0x3f3f3f3f;
27         ok = 0;
28         for(int start=0; start<=m-n+1; ++start)
29         {
30             for(int i=1; i<=n; ++i)
31                 cnt[i] = i;
32             int i, j = 0;
33             for(i=start; i<m && j<n-1; ++i)
34             {
35                 a = Find(edge[i].from);
36                 b = Find(edge[i].to);
37                 if(a != b)
38                     cnt[b] = a, ++j;
39             }
40             if(j == n-1)
41                 MIN = min(MIN, edge[i-1].distance - edge[start].distance), ok = 1;
42         }
43         printf("%d\n", ok ? MIN : -1);
44     }
45 }

 

posted @ 2015-09-03 16:18  Corvey  阅读(151)  评论(0)  编辑  收藏  举报