uva 1395 苗条的生成树（最小生成树入门）

补一下图论知识...

题意：给n个点，m条边，求所有生成树中：边权最大值-  边权最小值 的结果最小

思路：区间做一遍最小生成树，每次记录成功的左端点和右端点，维护最小值就可以了。

(用了kuangbin的模板)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#define INF 0x3fffffff
using namespace std;

const int MAXN = 110;  //最大点数
const int MAXM = 10000;//最大边数

int F[MAXN];
struct Edge{
int u,v,w;
}edge[MAXM];
int tol;
void addedge(int m){
//    edge[tol].u = u;
//    edge[tol].v = v;
//    edge[tol++].w = w;
for(int i =0;i<m;i++){
int u,v,w;
scanf("%d%d%d",&u,&v,&w);
//addedge(u,v,w);
edge[i].u = u;
edge[i].v = v;
edge[i].w = w;
}
tol = m;
}
bool cmp(Edge a,Edge b){
return a.w < b.w;
}
int find(int x){
return F[x] == -1? x : F[x] = find(F[x]);
}
int kruskal(int n){

sort(edge,edge+tol,cmp);
int ans = INF;

for(int i = 0;i<tol;i++){

int low = edge[i].w,high = 0;
int cnt = 0;
memset(F,-1,sizeof F);

for(int j =i;j<tol;j++){
int u = edge[j].u;
int v = edge[j].v;
int w = edge[j].w;
int t1 = find(u);
int t2 = find(v);
if(t1!=t2){
cnt++;
F[t1] = t2;high = w;
}
if(cnt == n-1)
ans = min(high - low,ans);
}
}
if(ans == INF) ans = -1;
return ans;
}
int n,m;
int main()
{
//freopen("in.txt","r",stdin);
while(~scanf("%d%d",&n,&m) && !(n==m&&n == 0)){
addedge(m);
printf("%d\n",kruskal(n));

}
return 0;
}