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

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 }