New Algorithm: Parity Outlier (#1314)

* [feat] New algorithm

* [test] Add new test for ParityOutlier.js

* [fix] Reset indentation

* [fix] Reset indentation

* [fix] Style changes

* fix: improve code efficiency and a glitch

* test: adds a new possible test case

* fix: style fix

* fix: delete redundant comments and else statements

* [fix] style fix

Author: mrmagic2020

Maths/ParityOutlier.js

@@ -0,0 +1,33 @@
+/**
+ * @author mrmagic2020
+ * @description The function will find the parity outlier from an array of integers.
+ * @see https://en.wikipedia.org/wiki/Parity_(mathematics)
+ * @param {number[]} integers - An array of integers.
+ * @returns {number} - The parity outlier.
+ * @example parityOutlier([1, 3, 5, 8, 9]) = 8
+ */
+const parityOutlier = (integers) => {
+  let oddsCount = 0 // define counter for odd number(s)
+  let evensCount = 0 // define counter for even number(s)
+  let odd, even
+
+  for (const e of integers) {
+    if (!Number.isInteger(e)) { // detect non-integer elements
+      return null
+    }
+    if (e % 2 === 0) { // an even number
+      even = e
+      evensCount++
+    } else { // an odd number
+      odd = e
+      oddsCount++
+    }
+  }
+
+  if (oddsCount === 0 || evensCount === 0) return null // array has only odd/even number(s)
+  if (oddsCount > 1 && evensCount > 1) return null // array has more than one even and odd number
+
+  return oddsCount === 1 ? odd : even
+}
+
+export { parityOutlier }

Maths/test/ParityOutlier.test.js

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+import { parityOutlier } from '../ParityOutlier'
+
+describe('Testing parityOutlier function', () => {
+  it('should return the odd number in an array of even numbers', () => {
+    expect(parityOutlier([1, 2, 16, -8848, 5126])).toBe(1)
+  })
+
+  it('should return the even number in an array of odd numbers', () => {
+    expect(parityOutlier([177, 5, 76, 1919])).toBe(76)
+  })
+
+  it('should, if the given array has only one integer element, return the integer itself', () => {
+    expect(parityOutlier([83])).toBe(83)
+    expect(parityOutlier([54])).toBe(54)
+  })
+
+  it('should, if the given array has only an odd and an even number, return the odd outlier', () => {
+    expect(parityOutlier([1, 2])).toBe(1)
+    expect(parityOutlier([4, 3])).toBe(3)
+  })
+
+  it('should return null if the given array is empty, contains only one integer, contains non-interger elements or does not have a parity outlier', () => {
+    expect(parityOutlier([])).toBe(null)
+    expect(parityOutlier([2])).toBe(null)
+    expect(parityOutlier([2, {}, 5, 'GitHub'])).toBe(null)
+    expect(parityOutlier([1, 3, 5, 7, 9])).toBe(null)
+    expect(parityOutlier([0, 2, 4, 6, 8])).toBe(null)
+    expect(parityOutlier([1, 3, 5, 7, 2, 4, 6, 8])).toBe(null)
+  })
+})