basant307/AI_Governance_Project

1/**2 * Obliterator Permutations Function3 * ==================================4 *5 * Iterator returning permutations of the given array.6 */7var Iterator = require('./iterator.js');8 9/**10 * Helper mapping indices to items.11 */12function indicesToItems(target, items, indices, r) {13  for (var i = 0; i < r; i++) target[i] = items[indices[i]];14}15 16/**17 * Permutations.18 *19 * @param  {array}    array - Target array.20 * @param  {number}   r     - Size of the subsequences.21 * @return {Iterator}22 */23module.exports = function permutations(array, r) {24  if (!Array.isArray(array))25    throw new Error(26      'obliterator/permutations: first argument should be an array.'27    );28 29  var n = array.length;30 31  if (arguments.length < 2) r = n;32 33  if (typeof r !== 'number')34    throw new Error(35      'obliterator/permutations: second argument should be omitted or a number.'36    );37 38  if (r > n)39    throw new Error(40      'obliterator/permutations: the size of the subsequences should not exceed the length of the array.'41    );42 43  var indices = new Uint32Array(n),44    subsequence = new Array(r),45    cycles = new Uint32Array(r),46    first = true,47    i;48 49  for (i = 0; i < n; i++) {50    indices[i] = i;51 52    if (i < r) cycles[i] = n - i;53  }54 55  i = r;56 57  return new Iterator(function next() {58    if (first) {59      first = false;60      indicesToItems(subsequence, array, indices, r);61      return {value: subsequence, done: false};62    }63 64    var tmp, j;65 66    i--;67 68    if (i < 0) return {done: true};69 70    cycles[i]--;71 72    if (cycles[i] === 0) {73      tmp = indices[i];74 75      for (j = i; j < n - 1; j++) indices[j] = indices[j + 1];76 77      indices[n - 1] = tmp;78 79      cycles[i] = n - i;80      return next();81    } else {82      j = cycles[i];83      tmp = indices[i];84 85      indices[i] = indices[n - j];86      indices[n - j] = tmp;87 88      i = r;89 90      indicesToItems(subsequence, array, indices, r);91      return {value: subsequence, done: false};92    }93  });94};95