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Simplify permutateWithoutRepetitions algorithm.

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Oleksii Trekhleb
2018-06-29 12:23:26 +03:00
parent db7ab9e299
commit 00f75028bf
2 changed files with 41 additions and 52 deletions
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32
src/algorithms/sets/permutations/permutateWithoutRepetitions.js
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@@ -3,35 +3,27 @@
* @return {*[]}
*/
export default function permutateWithoutRepetitions(permutationOptions) {
if (permutationOptions.length === 0) {
return [];
}
if (permutationOptions.length === 1) {
return [permutationOptions];
}
// Init permutations array.
const permutations = [];
// Get all permutations of length (n - 1).
const previousOptions = permutationOptions.slice(0, permutationOptions.length - 1);
const previousPermutations = permutateWithoutRepetitions(previousOptions);
// Get all permutations for permutationOptions excluding the first element.
const smallerPermutations = permutateWithoutRepetitions(permutationOptions.slice(1));
// Insert last option into every possible position of every previous permutation.
const lastOption = permutationOptions.slice(permutationOptions.length - 1);
// Insert first option into every possible position of every smaller permutation.
const firstOption = permutationOptions[0];
for (
let permutationIndex = 0;
permutationIndex < previousPermutations.length;
permutationIndex += 1
) {
const currentPermutation = previousPermutations[permutationIndex];
for (let permIndex = 0; permIndex < smallerPermutations.length; permIndex += 1) {
const smallerPermutation = smallerPermutations[permIndex];
// Insert last option into every possible position of currentPermutation.
for (let positionIndex = 0; positionIndex <= currentPermutation.length; positionIndex += 1) {
const permutationPrefix = currentPermutation.slice(0, positionIndex);
const permutationSuffix = currentPermutation.slice(positionIndex);
permutations.push(permutationPrefix.concat(lastOption, permutationSuffix));
// 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));
}
}