static long kBitDifferencePairs ( int arr [ ] , int n , int k ) {
  int MAX = Arrays . stream ( arr ) . max ( ) . getAsInt ( ) ;
  long [ ] count = new long [ MAX + 1 ] ;
  Arrays . fill ( count , 0 ) ;
  for ( int i = 0 ;
  i < n ;
  ++ i ) ++ count [ arr [ i ] ] ;
  long ans = 0 ;
  if ( k == 0 ) {
    for ( int i = 0 ;
    i <= MAX ;
    ++ i ) ans += ( count [ i ] * ( count [ i ] - 1 ) ) / 2 ;
    return ans ;
  }
  for ( int i = 0 ;
  i <= MAX ;
  ++ i ) {
    if ( count [ i ] == 0 ) continue ;
    for ( int j = i + 1 ;
    j <= MAX ;
    ++ j ) {
      if ( Integer . bitCount ( i ^ j ) == k ) ans += count [ i ] * count [ j ] ;
    }
  }
  return ans ;
}

static long kBitDifferencePairs ( int arr [ ] , int n , int k ) { int MAX = Arrays . stream ( arr ) . max ( ) . getAsInt ( ) ; long [ ] count = new long [ MAX + 1 ] ; Arrays . fill ( count , 0 ) ; for ( int i = 0 ; i < n ; ++ i ) ++ count [ arr [ i ] ] ; long ans = 0 ; if ( k == 0 ) { for ( int i = 0 ; i <= MAX ; ++ i ) ans += ( count [ i ] * ( count [ i ] - 1 ) ) / 2 ; return ans ; } for ( int i = 0 ; i <= MAX ; ++ i ) { if ( count [ i ] == 0 ) continue ; for ( int j = i + 1 ; j <= MAX ; ++ j ) { if ( Integer . bitCount ( i ^ j ) == k ) ans += count [ i ] * count [ j ] ; } } return ans ; }
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