javascript-algorithms/src/algorithms/sets/permutations/permutateWithoutRepetitions.js

/**
 * @param {*[]} permutationOptions
 * @return {*[]}
 */
export default function permutateWithoutRepetitions(permutationOptions) {
  if (permutationOptions.length === 1) {
    return [permutationOptions];
  }

  // Init permutations array.
  const permutations = [];

  // Get all permutations for permutationOptions excluding the first element.
  const smallerPermutations = permutateWithoutRepetitions(permutationOptions.slice(1));

  // Insert first option into every possible position of every smaller permutation.
  const firstOption = permutationOptions[0];

  for (let permIndex = 0; permIndex < smallerPermutations.length; permIndex += 1) {
    const smallerPermutation = smallerPermutations[permIndex];

    // Insert first option into every possible position of smallerPermutation.
    for (let positionIndex = 0; positionIndex <= smallerPermutation.length; positionIndex += 1) {
      const permutationPrefix = smallerPermutation.slice(0, positionIndex);
      const permutationSuffix = smallerPermutation.slice(positionIndex);
      permutations.push(permutationPrefix.concat([firstOption], permutationSuffix));
    }
  }

  return permutations;
}