static int countPairs ( int arr1 [ ] , int arr2 [ ] , int m , int n , int x ) {
  int count = 0 ;
  HashSet < Integer > us = new HashSet < Integer > ( ) ;
  for ( int i = 0 ;
  i < m ;
  i ++ ) us . add ( arr1 [ i ] ) ;
  for ( int j = 0 ;
  j < n ;
  j ++ ) if ( us . contains ( x - arr2 [ j ] ) ) count ++ ;
  return count ;
}

static int countPairs ( int arr1 [ ] , int arr2 [ ] , int m , int n , int x ) { int count = 0 ; HashSet < Integer > us = new HashSet < Integer > ( ) ; for ( int i = 0 ; i < m ; i ++ ) us . add ( arr1 [ i ] ) ; for ( int j = 0 ; j < n ; j ++ ) if ( us . contains ( x - arr2 [ j ] ) ) count ++ ; return count ; }
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