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/** * Implementation of Combinations * Combinations are unique subsets of a collection - in this case, k x from a collection at a time. * https://en.wikipedia.org/wiki/Combination * @param {Array} x any type of data * @param {int} k the number of objects in each group (without replacement) * @returns {Array<Array>} array of permutations * @example * combinations([1, 2, 3], 2); // => [[1,2], [1,3], [2,3]] */
function combinations(x, k) {    let i;    let subI;    const combinationList = [];    let subsetCombinations;    let next;
    for (i = 0; i < x.length; i++) {        if (k === 1) {            combinationList.push([x[i]]);        } else {            subsetCombinations = combinations(x.slice(i + 1, x.length), k - 1);            for (subI = 0; subI < subsetCombinations.length; subI++) {                next = subsetCombinations[subI];                next.unshift(x[i]);                combinationList.push(next);            }        }    }    return combinationList;}
export default combinations;