Fix zero-length combinations

Author: Sean-Kenneth-Doherty

src/algorithms/sets/combinations/__test__/combineWithRepetitions.test.js

@@ -3,6 +3,10 @@ import factorial from '../../../math/factorial/factorial';
 
 describe('combineWithRepetitions', () => {
   it('should combine string with repetitions', () => {
+    expect(combineWithRepetitions(['A', 'B'], 0)).toEqual([
+      [],
+    ]);
+
     expect(combineWithRepetitions(['A'], 1)).toEqual([
       ['A'],
     ]);
@@ -25,6 +29,8 @@ describe('combineWithRepetitions', () => {
       ['B', 'B', 'B'],
     ]);
 
+    expect(combineWithRepetitions(['A', 'B'], -1)).toEqual([]);
+
     expect(combineWithRepetitions(['A', 'B', 'C'], 2)).toEqual([
       ['A', 'A'],
       ['A', 'B'],

src/algorithms/sets/combinations/__test__/combineWithoutRepetitions.test.js

@@ -4,6 +4,10 @@ import pascalTriangle from '../../../math/pascal-triangle/pascalTriangle';
 
 describe('combineWithoutRepetitions', () => {
   it('should combine string without repetitions', () => {
+    expect(combineWithoutRepetitions(['A', 'B'], 0)).toEqual([
+      [],
+    ]);
+
     expect(combineWithoutRepetitions(['A', 'B'], 3)).toEqual([]);
 
     expect(combineWithoutRepetitions(['A', 'B'], 1)).toEqual([
@@ -29,6 +33,8 @@ describe('combineWithoutRepetitions', () => {
       ['A', 'B', 'C'],
     ]);
 
+    expect(combineWithoutRepetitions(['A', 'B', 'C'], -1)).toEqual([]);
+
     expect(combineWithoutRepetitions(['A', 'B', 'C', 'D'], 3)).toEqual([
       ['A', 'B', 'C'],
       ['A', 'B', 'D'],

src/algorithms/sets/combinations/combineWithRepetitions.js

@@ -4,6 +4,14 @@
  * @return {*[]}
  */
 export default function combineWithRepetitions(comboOptions, comboLength) {
+  if (comboLength === 0) {
+    return [[]];
+  }
+
+  if (comboLength < 0) {
+    return [];
+  }
+
   // If the length of the combination is 1 then each element of the original array
   // is a combination itself.
   if (comboLength === 1) {

src/algorithms/sets/combinations/combineWithoutRepetitions.js

@@ -4,6 +4,14 @@
  * @return {*[]}
  */
 export default function combineWithoutRepetitions(comboOptions, comboLength) {
+  if (comboLength === 0) {
+    return [[]];
+  }
+
+  if (comboLength < 0) {
+    return [];
+  }
+
   // If the length of the combination is 1 then each element of the original array
   // is a combination itself.
   if (comboLength === 1) {