feat: add dutchNationalFlagSort implementation (TheAlgorithms#1305)

* feat: add dutchNationalFlagSort implementation

* fix: add test, fit code style

* fix: add link to directory.md

DIRECTORY.md

@@ -303,6 +303,7 @@
   * [CombSort](Sorts/CombSort.js)
   * [CountingSort](Sorts/CountingSort.js)
   * [CycleSort](Sorts/CycleSort.js)
+  * [DutchNationalFlagSort](Sorts/DutchNationalFlagSort.js)
   * [FindSecondLargestElement](Sorts/FindSecondLargestElement.js)
   * [FisherYatesShuffle](Sorts/FisherYatesShuffle.js)
   * [FlashSort](Sorts/FlashSort.js)

Sorts/DutchNationalFlagSort.js

@@ -0,0 +1,33 @@
+/**
+ * @function dutchNationalFlagSort
+ * @description Dutch National Flag Sort is an algorithm to sort an array containing 0s, 1s, and 2s in linear time.
+    Time complexity of Dutch National Flag Sort Algorithm is O(n).
+    Auxiliary Space required for Dutch National Flag Sort Algorithm is O(1).
+ * @param {Integer[]} nums - Array of integers containing 0s, 1s, and 2s.
+ * @return {Integer[]} - Array of integers sorted in non-decreasing order.
+ * @see [Dutch National Flag Sort](https://en.wikipedia.org/wiki/Dutch_national_flag_problem)
+ */
+export function dutchNationalFlagSort (nums) {
+  let low = 0
+  let mid = 0
+  let high = nums.length - 1
+
+  while (mid <= high) {
+    switch (nums[mid]) {
+      case 0:
+        [nums[low], nums[mid]] = [nums[mid], nums[low]]
+        low++
+        mid++
+        break
+      case 1:
+        mid++
+        break
+      case 2:
+        [nums[mid], nums[high]] = [nums[high], nums[mid]]
+        high--
+        break
+    }
+  }
+
+  return nums
+}

Sorts/test/DutchNationalFlagSort.test.js

@@ -0,0 +1,9 @@
+import { dutchNationalFlagSort } from '../DutchNationalFlagSort'
+
+describe('DutchNationalFlagSort', () => {
+  it('should sort arrays correctly', () => {
+    expect(dutchNationalFlagSort([2, 0, 2, 1, 1, 0])).toEqual([0, 0, 1, 1, 2, 2])
+    expect(dutchNationalFlagSort([2, 1, 0])).toEqual([0, 1, 2])
+    expect(dutchNationalFlagSort([1, 0, 0, 0, 1])).toEqual([0, 0, 0, 1, 1])
+  })
+})