combineWithRepetitions.test.js

import combineWithRepetitions from '../combineWithRepetitions';
import factorial from '../../../math/factorial/factorial';

describe('combineWithRepetitions', () => {
  it('should combine string with repetitions', () => {
    expect(combineWithRepetitions(['A'], 1)).toEqual([
      ['A'],
    ]);

    expect(combineWithRepetitions(['A', 'B'], 1)).toEqual([
      ['A'],
      ['B'],
    ]);

    expect(combineWithRepetitions(['A', 'B'], 2)).toEqual([
      ['A', 'A'],
      ['A', 'B'],
      ['B', 'B'],
    ]);

    expect(combineWithRepetitions(['A', 'B'], 3)).toEqual([
      ['A', 'A', 'A'],
      ['A', 'A', 'B'],
      ['A', 'B', 'B'],
      ['B', 'B', 'B'],
    ]);

    expect(combineWithRepetitions(['A', 'B', 'C'], 2)).toEqual([
      ['A', 'A'],
      ['A', 'B'],
      ['A', 'C'],
      ['B', 'B'],
      ['B', 'C'],
      ['C', 'C'],
    ]);

    expect(combineWithRepetitions(['A', 'B', 'C'], 3)).toEqual([
      ['A', 'A', 'A'],
      ['A', 'A', 'B'],
      ['A', 'A', 'C'],
      ['A', 'B', 'B'],
      ['A', 'B', 'C'],
      ['A', 'C', 'C'],
      ['B', 'B', 'B'],
      ['B', 'B', 'C'],
      ['B', 'C', 'C'],
      ['C', 'C', 'C'],
    ]);

    const combinationOptions = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H'];
    const combinationSlotsNumber = 4;
    const combinations = combineWithRepetitions(combinationOptions, combinationSlotsNumber);
    const n = combinationOptions.length;
    const r = combinationSlotsNumber;
    const expectedNumberOfCombinations = factorial((r + n) - 1) / (factorial(r) * factorial(n - 1));

    expect(combinations.length).toBe(expectedNumberOfCombinations);
  });
});