public static int longestAr ( int n , int arr [ ] ) {
  Hashtable < Integer , Integer > count = new Hashtable < Integer , Integer > ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( count . containsKey ( arr [ i ] ) ) count . put ( arr [ i ] , count . get ( arr [ i ] ) + 1 ) ;
    else count . put ( arr [ i ] , 1 ) ;
  }
  Set < Integer > kset = count . keySet ( ) ;
  Iterator < Integer > it = kset . iterator ( ) ;
  int max = 0 ;
  while ( it . hasNext ( ) ) {
    int a = ( int ) it . next ( ) ;
    int cur = 0 ;
    int cur1 = 0 ;
    int cur2 = 0 ;
    if ( count . containsKey ( a + 1 ) ) cur1 = count . get ( a + 1 ) ;
    if ( count . containsKey ( a - 1 ) ) cur2 = count . get ( a - 1 ) ;
    cur = count . get ( a ) + Math . max ( cur1 , cur2 ) ;
    if ( cur > max ) max = cur ;
  }
  return ( max ) ;
}

public static int longestAr ( int n , int arr [ ] ) { Hashtable < Integer , Integer > count = new Hashtable < Integer , Integer > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { if ( count . containsKey ( arr [ i ] ) ) count . put ( arr [ i ] , count . get ( arr [ i ] ) + 1 ) ; else count . put ( arr [ i ] , 1 ) ; } Set < Integer > kset = count . keySet ( ) ; Iterator < Integer > it = kset . iterator ( ) ; int max = 0 ; while ( it . hasNext ( ) ) { int a = ( int ) it . next ( ) ; int cur = 0 ; int cur1 = 0 ; int cur2 = 0 ; if ( count . containsKey ( a + 1 ) ) cur1 = count . get ( a + 1 ) ; if ( count . containsKey ( a - 1 ) ) cur2 = count . get ( a - 1 ) ; cur = count . get ( a ) + Math . max ( cur1 , cur2 ) ; if ( cur > max ) max = cur ; } return ( max ) ; }
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