public static void main ( String [ ] args ) throws IOException {
  int t = input . nextInt ( ) ;
  int [ ] a = new int [ 105 ] ;
  Set < Integer > st = new HashSet < Integer > ( ) ;
  while ( t -- != 0 ) {
    st . clear ( ) ;
    int n = input . nextInt ( ) ;
    int k = input . nextInt ( ) ;
    for ( int i = 0 ;
    i < n ;
    i ++ ) {
      int x = input . nextInt ( ) ;
      st . add ( x ) ;
    }
    int cnt = st . size ( ) ;
    if ( k == 1 && cnt > 1 ) {
      pr . println ( - 1 ) ;
      continue ;
    }
    if ( cnt <= k ) {
      pr . println ( 1 ) ;
      continue ;
    }
    pr . println ( 1 + ( cnt - 2 ) / ( k - 1 ) ) ;
  }
  pr . flush ( ) ;
}

public static void main ( String [ ] args ) throws IOException { int t = input . nextInt ( ) ; int [ ] a = new int [ 105 ] ; Set < Integer > st = new HashSet < Integer > ( ) ; while ( t -- != 0 ) { st . clear ( ) ; int n = input . nextInt ( ) ; int k = input . nextInt ( ) ; for ( int i = 0 ; i < n ; i ++ ) { int x = input . nextInt ( ) ; st . add ( x ) ; } int cnt = st . size ( ) ; if ( k == 1 && cnt > 1 ) { pr . println ( - 1 ) ; continue ; } if ( cnt <= k ) { pr . println ( 1 ) ; continue ; } pr . println ( 1 + ( cnt - 2 ) / ( k - 1 ) ) ; } pr . flush ( ) ; }
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