permute/index.js

A tiny library to permutate a sequence.

/*
 * Copyright (c) 2013, Ben Noordhuis <info@bnoordhuis.nl>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

module.exports = permute;

function permute(seq)
{
  var i, j, v;
  var end;

  if (seq.length <= 1) {
    return false;
  }

  i = end = seq.length - 1;
  for (;;) {
    v = seq[i];
    i -= 1;

    if (seq[i] < v) {
      v = seq[i];
      for (j = end; seq[j] < v; j -= 1);
      swap(seq, i, j);
      reverse(seq, i + 1, end);
      return true;
    }

    if (i === 0) {
      reverse(seq, 0, end);
      return false;
    }
  }

  return true;
}

function reverse(seq, start, end)
{
  while (start < end) {
    swap(seq, start, end);
    start += 1;
    end -= 1;
  }
}

function swap(seq, i, j)
{
  var t = seq[i];
  seq[i] = seq[j];
  seq[j] = t;
}