BZOJ 3943: [Usaco2015 Feb]SuperBull 最小生成树

// luogu-judger-enable-o2
#include<bits/stdc++.h>
#define setIO(s) freopen(s".in","r",stdin) 
#define maxn 4100000
#define ll long long 
using namespace std;
int u[maxn],v[maxn],p[3000],A[maxn];  
ll arr[3000],val[maxn]; 
int n,edges; 
int find(int x)
{
    return p[x]==x?x:p[x]=find(p[x]); 
}
bool merge(int a,int b)
{
    int x=find(a),y=find(b);
    if(x==y) return false;
    p[x]=y;
    return true; 
}
bool cmp(const int i,const int j)
{
    return val[i]>val[j]; 
}
int main()
{
   //  setIO("input"); 
    scanf("%d",&n);
    for(int i=0;i<3000;++i) p[i]=i; 
    for(int i=1;i<=n;++i) scanf("%lld",&arr[i]); 
    for(int i=1;i<=n;++i)
        for(int j=1;j<=n;++j)
        {
            if(i==j) continue;                
            A[++edges]=edges, u[edges]=i,v[edges]=j, val[edges]=arr[i]^arr[j]; 
        }
    sort(A+1,A+1+edges,cmp); 
    ll sum=0;
    int cc=0;
    for(int i=1;i<=edges;++i)
    {
        int e=A[i];
        int a=u[e],b=v[e];
        if(merge(a,b)) sum+=val[e],++cc; 
        if(cc==n-1) break; 
    }
    printf("%lld\n",sum); 
    return 0; 
}