曼哈顿最小生成树

struct point
{
    int x,y,id;
    friend bool operator<( const point&a ,const point&b )
    {
        if ( a.x!=b.x ) return a.x<b.x;
        else return a.y<b.y;
    }
}p[maxn];
int n,m,tol,pre[maxn],minx[maxn],posx[maxn];
int Find( int x ){ return x==pre[x]?pre[x]:pre[x]=Find(pre[x]); }
struct edge
{
    int u,v,cost;
    friend bool operator<( const edge&a , const edge&b )
    {
        return a.cost<b.cost;
    }
}es[maxm];
void addedge( int u , int v , int w )
{
    es[tol].u = u;
    es[tol].v = v;
    es[tol].cost = w;
    tol++;
}
void update( int i , int val , int pos )
{
    for ( ; i>=1 ; i-=lowbit(i) )
    {
        if ( val<minx[i] )
        {
            minx[i] = val;
            posx[i] = pos;
        }
    }
}
int ask( int i )
{
    int min_val = inf,pos = -1;
    for ( ; i<=m ; i+=lowbit(i) )
    {
        if ( minx[i]<min_val )
            min_val = minx[i],pos = posx[i];
    }
    return pos;
}
void manhattan()
{
    int a[maxn],b[maxn]; tol = 0;
    for ( int dir=0 ; dir<4 ; dir++ )
    {
        if ( dir==1||dir==3 )
        {
            for ( int i=0 ; i<n ; i++ )
                swap ( p[i].x , p[i].y );
        }
        else if ( dir==2 )
        {
            for ( int i=0 ; i<n ; i++ )
                p[i].x = -p[i].x;
        }
        sort ( p , p+n );
        for ( int i=0 ; i<n ; i++ )
            a[i] = b[i] = p[i].y-p[i].x;
        sort ( b , b+n );
        m = unique( b , b+n )-b;
        for ( int i=1 ; i<=m ; i++ )
            minx[i] = inf,posx[i] = -1;
        for ( int i=n-1 ; i>=0 ; i-- )
        {
            int pos = lower_bound( b , b+m , a[i] )-b+1;
            int ans = ask( pos );
            if ( ans!=-1 )
                addedge( p[i].id , p[ans].id , Abs(p[i].x-p[ans].x)+Abs(p[i].y-p[ans].y) );
            update( pos , p[i].x+p[i].y , i );
        }
    }
}
int solve( int k )
{
    manhattan();
    for ( int i=0 ; i<n ; i++ ) pre[i] = i;
    sort( es , es+tol );
    for ( int i=0 ; i<tol ; i++ )
    {
        int u = es[i].u;
        int v = es[i].v;
        int fx = Find(u);
        int fy = Find(v);
        if ( fx!=fy )
        {
            pre[fx] = fy;
            k--;
            if ( k==0 ) return es[i].cost;
        }
    }
}