combineWithoutRepetitions.js

/**
 * @param {*[]} comboOptions
 * @param {number} comboLength
 * @return {*[]}
 */
export default function combineWithoutRepetitions(comboOptions, comboLength) {
 // If the length of the combination is 1 then each element of the original array
 // is a combination itself.
 if (comboLength === 1) {
 return comboOptions.map((comboOption) => [comboOption]);
 }

 // Init combinations array.
 const combos = [];

 // Extract characters one by one and concatenate them to combinations of smaller lengths.
 // We need to extract them because we don't want to have repetitions after concatenation.
 comboOptions.forEach((currentOption, optionIndex) => {
 // Generate combinations of smaller size.
 const smallerCombos = combineWithoutRepetitions(
 comboOptions.slice(optionIndex + 1),
 comboLength - 1,
 );

 // Concatenate currentOption with all combinations of smaller size.
 smallerCombos.forEach((smallerCombo) => {
 combos.push([currentOption].concat(smallerCombo));
 });
 });

 return combos;
}