It's changed for python3 and comments are added

Programming Assignment 3/QuickSort.py

@@ -1,26 +1,31 @@
+#It's written in python3
 
-with open('QuickSort.txt') as f:
+with open('c:/Users/Nabin/Desktop/output.txt') as f:
     a = [int(x) for x in f]
 
-def FindMedian(A):
+
+#It's for the 3rd part of the assignment where we are told to use the median of three
+def FindMedian(A): 
     minvalue = min(A)
     maxvalue = max(A)
     for i in range(3):
         if A[i] != minvalue and A[i] != maxvalue:
             return A[i]
 
+
+#It's a function which chooses the pivot either the first elem for flag1, the last for flag2 and the median of three for flag3
 def ChoosePivot(A,flag):
     n = len(A)
     first = A[0]
     final = A[n-1]
-    if n/2*2==n:
-        k = n/2 - 1
+    if(n%2==0):
+        k = n//2 - 1
         middle = A[k]
-    elif n/2*2<n:
-        k = n/2
+    elif(n%2!=0):
+        k = n//2
         middle = A[k]
     else:
-        print 'error in ChoosePivot to choose middle element of A'
+        print('error in ChoosePivot to choose middle element of A')
 
     B = [first,middle,final]
     med = FindMedian(B)
@@ -38,15 +43,17 @@ def ChoosePivot(A,flag):
     if flag==3:
         return position
     else:
-        print 'wrong flag'
+        print('wrong flag')
 
+#Just a normal swap function
 def Swap(A,first,second):
     second_value = A[second]
     first_value = A[first]
     A[first] = second_value
     A[second] = first_value
     return A
 
+#It's where the main work is done.Comparing the elements. Here we always use the first element as a pivot than continue our comparison and swap.It places the the pivot value in it's proper position in the list
 def Partition(A):
     pivot = A[0]
     r = len(A)
@@ -57,17 +64,19 @@ def Partition(A):
             i +=1
     A = Swap(A,0,i-1)
     return A,i-1
-
+
+
+#The main function where recursion is called
 def QuickSort(A,flag):
     n = len(A)
 
     if n>1:
         p = ChoosePivot(A,flag)
-        A = Swap(A,0,p)
+        A = Swap(A,0,p) #places the pivot element in the first position as our partition function works assuming the first element is the pivot.
         A,pivot_position = Partition(A)
         A[:pivot_position],left = QuickSort(A[:pivot_position],flag)
         A[pivot_position+1:],right = QuickSort(A[pivot_position+1:],flag)
 
-        return A,left+right+n-1
+        return A,left+right+n-1 #for each recursive call atleast n-1 comparison is made and then it works for the left and right sublist.
     else:
         return A,0