(* virt-similarity
 * Copyright (C) 2013 Red Hat Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *)

(* Returns all unique pairs of integers (i, j) = (0..n-1, 0..n-1) where i != j.
 * For example:
 * 'pairs_of_ints 3' returns [ (0,1); (0,2); (1,2) ]
 *)
let pairs_of_ints n =
  let ret = ref [] in
  for i = n-1 downto 0 do
    for j = i-1 downto 0 do
      ret := (j, i) :: !ret
    done
  done;
  !ret

(* Returns all pairs from lists 'xs' and 'ys'. *)
let pairs xs ys =
  let ret = ref [] in
  List.iter (fun x -> List.iter (fun y -> ret := (x, y) :: !ret) ys) xs;
  !ret