chore: merged "Quick select tests" (#697)

* add link to function description

* fix formatting for consistency

* export function so it can be imported for testing

* throw error on invalid input

* add tests for QuickSelect.js

* remove unnecessary comment

* Update Data-Structures/Array/QuickSelect.js

Co-authored-by: Rak Laptudirm <raklaptudirm@gmail.com>

Co-authored-by: Rak Laptudirm <raklaptudirm@gmail.com>

Data-Structures/Array/QuickSelect.js

@@ -1,5 +1,5 @@
 /**
- * QuickSelect is an algorithm to find the kth smallest number
+ * [QuickSelect](https://www.geeksforgeeks.org/quickselect-algorithm/) is an algorithm to find the kth smallest number
  *
  * Notes:
  * -QuickSelect is related to QuickSort, thus has optimal best and average
@@ -13,18 +13,13 @@
 
 function QuickSelect (items, kth) { // eslint-disable-line no-unused-vars
   if (kth < 1 || kth > items.length) {
-    return 'Index Out of Bound'
+    throw new RangeError('Index Out of Bound')
   }
 
   return RandomizedSelect(items, 0, items.length - 1, kth)
 }
 
-function RandomizedSelect (
-  items,
-  left,
-  right,
-  i
-) {
+function RandomizedSelect (items, left, right, i) {
   if (left === right) return items[left]
 
   const pivotIndex = RandomizedPartition(items, left, right)
@@ -76,3 +71,5 @@ function Swap (arr, x, y) {
 // "Index Out of Bound"
 // > QuickSelect([1, 4, 2, -2, 4, 5], 7)
 // "Index Out of Bound"
+
+export { QuickSelect }

Data-Structures/Array/QuickSelect.test.js

@@ -0,0 +1,49 @@
+import { QuickSelect } from './QuickSelect'
+
+describe('QuickSelect tests', () => {
+  it('should return the only element of a list of length 1', () => {
+    // Test a mix of number types (i.e., positive/negative, numbers with decimals, fractions)
+    expect(QuickSelect([100], 1)).toEqual(100)
+    expect(QuickSelect([-23], 1)).toEqual(-23)
+    expect(QuickSelect([2007.102], 1)).toEqual(2007.102)
+    expect(QuickSelect([0.9], 1)).toEqual(0.9)
+    expect(QuickSelect([-0.075], 1)).toEqual(-0.075)
+    expect(QuickSelect([0], 1)).toEqual(0)
+    expect(QuickSelect([1], 1)).toEqual(1)
+  })
+
+  it('should throw an Error when k is greater than the length of the list', () => {
+    expect(() => QuickSelect([100, 2], 5)).toThrow('Index Out of Bound')
+  })
+
+  it('should throw an Error when k is less than 1', () => {
+    expect(() => QuickSelect([100, 2], 0)).toThrow('Index Out of Bound')
+    expect(() => QuickSelect([100, 2], -1)).toThrow('Index Out of Bound')
+  })
+
+  describe('varieties of list composition', () => {
+    it('should return the kth smallest element of a list that is in increasing order', () => {
+      expect(QuickSelect([10, 22, 33, 44, 55], 1)).toEqual(10)
+      expect(QuickSelect([10, 22, 33, 44, 55], 2)).toEqual(22)
+      expect(QuickSelect([10, 22, 33, 44, 55], 3)).toEqual(33)
+      expect(QuickSelect([10, 22, 33, 44, 55], 4)).toEqual(44)
+      expect(QuickSelect([10, 22, 33, 44, 55], 5)).toEqual(55)
+    })
+
+    it('should return the kth smallest element of an input list that is in decreasing order', () => {
+      expect(QuickSelect([82, 33.12, 4.0, 1], 1)).toEqual(1)
+      expect(QuickSelect([82, 33.12, 4.0, 1], 2)).toEqual(4.0)
+      expect(QuickSelect([82, 33.12, 4.0, 1], 2)).toEqual(4)
+      expect(QuickSelect([82, 33.12, 4.0, 1], 3)).toEqual(33.12)
+      expect(QuickSelect([82, 33.12, 4.0, 1], 4)).toEqual(82)
+    })
+
+    it('should return the kth smallest element of an input list that is no particular order', () => {
+      expect(QuickSelect([123, 14231, -10, 0, 15], 3)).toEqual(15)
+      expect(QuickSelect([0, 15, 123, 14231, -10], 3)).toEqual(15)
+      expect(QuickSelect([-10, 15, 123, 14231, 0], 3)).toEqual(15)
+      expect(QuickSelect([14231, 0, 15, 123, -10], 3)).toEqual(15)
+      expect(QuickSelect([14231, 0, 15, -10, 123], 3)).toEqual(15)
+    })
+  })
+})