static long countPairs ( int arr [ ] , int n ) {
  int countZero = 0 ;
  int countTwo = 0 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( arr [ i ] == 0 ) countZero ++ ;
    else if ( arr [ i ] == 2 ) countTwo ++ ;
  }
  long pair0 = ( countZero * ( countZero - 1 ) ) / 2 ;
  long pair2 = ( countTwo * ( countTwo - 1 ) ) / 2 ;
  return pair0 + pair2 ;
}

static long countPairs ( int arr [ ] , int n ) { int countZero = 0 ; int countTwo = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( arr [ i ] == 0 ) countZero ++ ; else if ( arr [ i ] == 2 ) countTwo ++ ; } long pair0 = ( countZero * ( countZero - 1 ) ) / 2 ; long pair2 = ( countTwo * ( countTwo - 1 ) ) / 2 ; return pair0 + pair2 ; }
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