From 40a94146af09e742bceebac0990a50fd356b499e Mon Sep 17 00:00:00 2001
From: DevAnuragT <anuragthakur2102@gmail.com>
Date: Wed, 2 Oct 2024 03:39:52 +0530
Subject: [PATCH] feat: improve space complexity of QuickSort algorithm

---
 Sorts/QuickSort.js | 61 ++++++++++++++++++++++++++++++++++------------
 1 file changed, 46 insertions(+), 15 deletions(-)

diff --git a/Sorts/QuickSort.js b/Sorts/QuickSort.js
index 3885054e36..4139854b55 100644
--- a/Sorts/QuickSort.js
+++ b/Sorts/QuickSort.js
@@ -1,30 +1,61 @@
 /**
  * @function QuickSort
  * @description Quick sort is a comparison sorting algorithm that uses a divide and conquer strategy.
+ * It sorts the array in place by using a partitioning technique instead of creating separate arrays.
  * @param {Integer[]} items - Array of integers
+ * @param {Integer} left - Starting index
+ * @param {Integer} right - Ending index
  * @return {Integer[]} - Sorted array.
  * @see [QuickSort](https://en.wikipedia.org/wiki/Quicksort)
  */
-function quickSort(items) {
-  const length = items.length
-
-  if (length <= 1) {
+function quickSort(items, left = 0, right = items.length - 1) {
+  if (left >= right) {
     return items
   }
-  const PIVOT = items[0]
-  const GREATER = []
-  const LESSER = []
-
-  for (let i = 1; i < length; i++) {
-    if (items[i] > PIVOT) {
-      GREATER.push(items[i])
-    } else {
-      LESSER.push(items[i])
+
+  const pivotIndex = partition(items, left, right)
+  quickSort(items, left, pivotIndex - 1)
+  quickSort(items, pivotIndex + 1, right)
+
+  return items
+}
+
+/**
+ * @function partition
+ * @description Partitions the array in place and returns the index of the pivot.
+ * @param {Integer[]} items - Array of integers
+ * @param {Integer} left - Starting index
+ * @param {Integer} right - Ending index
+ * @return {Integer} - Pivot index.
+ */
+function partition(items, left, right) {
+  const PIVOT = items[right] // Choose the rightmost element as pivot
+  let partitionIndex = left
+
+  for (let i = left; i < right; i++) {
+    if (items[i] < PIVOT) {
+      swap(items, i, partitionIndex)
+      partitionIndex++
     }
   }
 
-  const sorted = [...quickSort(LESSER), PIVOT, ...quickSort(GREATER)]
-  return sorted
+  // Move the pivot to its correct position
+  swap(items, partitionIndex, right)
+
+  return partitionIndex
+}
+
+/**
+ * @function swap
+ * @description Helper function to swap two elements in the array.
+ * @param {Integer[]} items - Array of integers
+ * @param {Integer} i - Index of the first element
+ * @param {Integer} j - Index of the second element
+ */
+function swap(items, i, j) {
+  const temp = items[i]
+  items[i] = items[j]
+  items[j] = temp
 }
 
 export { quickSort }