basant307/AI_Governance_Project

1/**2 * Obliterator Combinations Function3 * ==================================4 *5 * Iterator returning combinations 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 * Combinations.18 *19 * @param  {array}    array - Target array.20 * @param  {number}   r     - Size of the subsequences.21 * @return {Iterator}22 */23module.exports = function combinations(array, r) {24  if (!Array.isArray(array))25    throw new Error(26      'obliterator/combinations: first argument should be an array.'27    );28 29  var n = array.length;30 31  if (typeof r !== 'number')32    throw new Error(33      'obliterator/combinations: second argument should be omitted or a number.'34    );35 36  if (r > n)37    throw new Error(38      'obliterator/combinations: the size of the subsequences should not exceed the length of the array.'39    );40 41  if (r === n) return Iterator.of(array.slice());42 43  var indices = new Array(r),44    subsequence = new Array(r),45    first = true,46    i;47 48  for (i = 0; i < r; i++) indices[i] = i;49 50  return new Iterator(function next() {51    if (first) {52      first = false;53 54      indicesToItems(subsequence, array, indices, r);55      return {value: subsequence, done: false};56    }57 58    if (indices[r - 1]++ < n - 1) {59      indicesToItems(subsequence, array, indices, r);60      return {value: subsequence, done: false};61    }62 63    i = r - 2;64 65    while (i >= 0 && indices[i] >= n - (r - i)) --i;66 67    if (i < 0) return {done: true};68 69    indices[i]++;70 71    while (++i < r) indices[i] = indices[i - 1] + 1;72 73    indicesToItems(subsequence, array, indices, r);74    return {value: subsequence, done: false};75  });76};77