poj3522解题报告

题目大意：题意：给点一个无向图，求一个生成树使树中最大边与最小边的差的最小。

解题思路；首先按照边权排一次序，然后依次枚举最小的边权，利用kruskal算法生成无根树！！！（利用并查集维护集合关系）

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<vector>
#include<cstring>
using namespace std;
const int maxn=1e4;
const int INF=(1<<30);
int p[maxn],n,m,u,v,d;

struct Edge {
  int u, v, d;
  Edge(int u, int v, int d):u(u),v(v),d(d) {}
  bool operator < (const Edge& rhs) const {
    return d < rhs.d;
  }
};

void Make_Set(int n)
{
        for(int i=1;i<=n;i++)
                p[i]=i;
}

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

vector<Edge> e;

int main()
{
        //freopen("1.txt","r",stdin);
        while(scanf("%d%d",&n,&m)==2)
        {
                e.clear();
                if(m==0&&n==0)  break;
                for(int i=0;i<m;i++)
                {
                        scanf("%d%d%d",&u,&v,&d);
                        e.push_back(Edge(u,v,d));
                }
                sort(e.begin(),e.end());

                int ans=INF;
                for(int L=0;L<m;L++)
                {
                     Make_Set(n);
                     int cnt=0;
                     for(int R=L;R<m;R++)
                     {
                            int u=Find_Set(e[R].u);
                            int v=Find_Set(e[R].v);
                            if(u!=v)
                            {
                                    p[u]=v;
                                    cnt++;
                                    if(cnt==n-1){ans=min(ans,e[R].d-e[L].d);break;}
                            }
                     }
                }
                if(ans==INF)  printf("-1\n");
                else printf("%d\n",ans);
        }
        return 0;
}