Update Quick_sort.py

Author: ammalik221

Searching_and_Sorting/Quick_sort.py

@@ -6,25 +6,32 @@
 
 def quick_sort(arr, lower_index, upper_index):
 
+    # already sorted
     if lower_index >= upper_index:
         return
-      
+    
+    # selecting the last element as the pivot
     pivot = arr[-1]
     left = lower_index
     right = upper_index - 1
 
     while left <= right:
+        # keep increasing left until a number greater than pivot is found
         while left <= right and arr[left] < pivot:
             left += 1
-            
+        
+        # keep decreasing right until a number lesser than pivot is found
         while left <= right and arr[right] > pivot:
             right -= 1
 
         if left <= right:
+            # swapping the two numbers
             arr[left], arr[right] = arr[right], arr[left]
             left += 1
             right -= 1
-            
+    
+    # swap left element with pivot element,
+    # to bring the pivot element to its appropritate position
     arr[left], arr[upper_index] = arr[upper_index], arr[left]
     quick_sort(arr, 0, left-1)
     quick_sort(arr, left+1, upper_index)