Created MergeSort_linkedlist_in_python.py

Coding/MergeSort_linkedlist_in_python.py

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+# Python3 program to merge sort of linked list
+
+class Node:
+	def __init__(self, data):
+		self.data = data
+		self.next = None
+
+class LinkedList:
+	def __init__(self):
+		self.head = None
+
+	# push new value to linked list
+	def append(self, new_value):
+		new_node = Node(new_value)
+		if self.head is None:
+			self.head = new_node
+			return
+		curr_node = self.head
+		while curr_node.next is not None:
+			curr_node = curr_node.next
+
+		# Append the new node at the end
+		curr_node.next = new_node
+
+	def sortedMerge(self, a, b):
+		result = None
+
+		# Base cases
+		if a == None:
+			return b
+		if b == None:
+			return a
+
+		if a.data <= b.data:
+			result = a
+			result.next = self.sortedMerge(a.next, b)
+		else:
+			result = b
+			result.next = self.sortedMerge(a, b.next)
+		return result
+
+	def mergeSort(self, h):
+
+		# Base case if head is None
+		if h == None or h.next == None:
+			return h
+
+		# get the middle of the list
+		middle = self.getMiddle(h)
+		nexttomiddle = middle.next
+
+		middle.next = None
+
+		# Apply mergeSort on left list
+		left = self.mergeSort(h)
+
+		# Apply mergeSort on right list
+		right = self.mergeSort(nexttomiddle)
+
+		# Merge the left and right lists
+		sortedlist = self.sortedMerge(left, right)
+		return sortedlist
+
+	def getMiddle(self, head):
+		if (head == None):
+			return head
+
+		slow = head
+		fast = head
+
+		while (fast.next != None and
+			fast.next.next != None):
+			slow = slow.next
+			fast = fast.next.next
+
+		return slow
+
+def printList(head):
+	if head is None:
+		print(' ')
+		return
+	curr_node = head
+	while curr_node:
+		print(curr_node.data, end = " ")
+		curr_node = curr_node.next
+	print(' ')
+
+if __name__ == '__main__':
+	li = LinkedList()
+
+	li.append(15)
+	li.append(10)
+	li.append(5)
+	li.append(20)
+	li.append(3)
+	li.append(2)
+
+	# Apply merge Sort
+	li.head = li.mergeSort(li.head)
+	print ("Sorted Linked List is:")
+	printList(li.head)