uva 1395 苗条的树 slim tree 最小生成树 Kruskal

暴力枚举，时间复杂度为O(n^2)

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#define INF 0x3f3f3f3f
using namespace std;

typedef struct node{
	int s;
	int e;
	int w;
}node;

node edge[100005];
int p[10000];

bool cmp(node a, node b){
	return a.w < b.w;
}

int find(int x){
	return p[x]==x ? x:p[x]=find(p[x]);
}

int main()
{
	int n, m;
	while(scanf("%d%d", &n, &m))
	{
		if(!n && !m)	break;
		for(int i = 1; i <= m; i++)
			scanf("%d%d%d", &edge[i].s, &edge[i].e, &edge[i].w);
		sort(edge+1, edge+1+m, cmp);
		int ans = INF;
		for(int i = 1; i <= m; i++)
		{
			int cnt = 0;
			for(int k = 1; k <= n; k++)  p[k] = k;
			for(int j = i; j <= m; j++)
			{
				 int sta = edge[j].s;
				 int end = edge[j].e;
				 int fs = find(sta);
				 int fe = find(end);
				 if(fs != fe)
				 {
				 	cnt++;
				 	p[fs] = fe;
				 }
				 if(cnt == n-1)
				 {
				 	ans = min(ans, edge[j].w-edge[i].w);
				 	break;
				 }
			}
		}
		printf("%d\n", ans==INF ? -1:ans);
	}
	return 0;
}