/** Basic combinatorial utility. For internal use only. */
import { Primitive } from "./util";
/**
 * Return all k-combinations with repition from a given pool.
 *
 * For example if the pool is the array [1, 2, 3, 4] and k = 2 the result are
 * all multi-subarrays of length 2:
 *
 *   [1,1], [2,1], [3,1], [4,1], [2,2], [3,2], [4,2], [3,3], [4,3], [4,4].
 *
 * The elements are ordered lexicographically.
 *
 * Remark: If n is the length of the iterable, there are n+k-1 over k such
 * combinations.
 *
 * See also:
 * https://en.wikipedia.org/wiki/Combination#Number_of_combinations_with_repetition
 *
 * @param pool A finite sequence
 * @param k The length of the combinations: 1, 2, 3, ...
 */
export declare function combinationsWithRepitition<T extends Primitive>(pool: readonly T[], k: number): T[][];
/**
 * Return all k-combinations from a given sequence.
 *
 * For example if the pool is the array [1,2,3,4] and k = 2 the result are all
 * subsequences of length 2:
 *
 *   [1,2], [1,3], [1,4], [2,3], [2,4], [3,4].
 *
 * The ordering is given as follows: Start with the k-combination with minimal
 * indices (here [1,2]), then repeat the following: Generate the next
 * combination by selecting the right-most index which can be incremented by 1
 * without making the new combination invalid (and do that), until this is
 * impossible (then all possible k-combinations are visited).
 *
 * Throws in case k > length of iterable
 *
 * Remark: If n is the length of iterable, the number of generated
 * k-combinations is given by the binomal coefficient n over k.
 *
 * See also:
 * https://en.wikipedia.org/wiki/Combination#Enumerating_k-combinations
 *
 * @param pool A finite sequence
 * @param k The length of the combinations: 1, 2, 3, ...
 */
export declare function combinations<T extends Primitive>(pool: readonly T[], k: number): T[][];