Create sort_linked_list.py

linked_lists/sort_linked_list.py

@@ -0,0 +1,107 @@
+
+# Python program to sort a linked list 
+class LinkedList(object): 
+    def __init__(self): 
+        self.head = None
+
+    # Linked list Node 
+    class Node(object): 
+        def __init__(self, d): 
+            self.data = d 
+            self.next = None
+
+    def newNode(self, key): 
+        return self.Node(key) 
+
+    # This is the main function that sorts 
+    # the linked list. 
+    def sort(self): 
+        # Create 2 dummy nodes and initialise as 
+        # heads of linked lists 
+        Ahead = self.Node(0) 
+        Dhead = self.Node(0) 
+        # Split the list into lists 
+        self.splitList(Ahead, Dhead) 
+        Ahead = Ahead.next
+        Dhead = Dhead.next
+        # reverse the descending list 
+        Dhead = self.reverseList(Dhead) 
+        # merge the 2 linked lists 
+        self.head = self.mergeList(Ahead, Dhead) 
+
+    # Function to reverse the linked list 
+    def reverseList(self, Dhead): 
+        current = Dhead 
+        prev = None
+        while current != None: 
+            self._next = current.next
+            current.next = prev 
+            prev = current 
+            current = self._next 
+        Dhead = prev 
+        return Dhead 
+
+    # Function to print linked list 
+    def printList(self): 
+        temp = self.head 
+        while temp != None: 
+            print temp.data, 
+            temp = temp.next
+        print '' 
+
+    # A utility function to merge two sorted linked lists 
+    def mergeList(self, head1, head2): 
+        # Base cases 
+        if head1 == None: 
+            return head2 
+        if head2 == None: 
+            return head1 
+        temp = None
+        if head1.data < head2.data: 
+            temp = head1 
+            head1.next = self.mergeList(head1.next, head2) 
+        else: 
+            temp = head2 
+            head2.next = self.mergeList(head1, head2.next) 
+        return temp 
+
+    # This function alternatively splits a linked list with head 
+    # as head into two: 
+    # For example, 10->20->30->15->40->7 is splitted into 10->30->40 
+    # and 20->15->7 
+    # "Ahead" is reference to head of ascending linked list 
+    # "Dhead" is reference to head of descending linked list 
+    def splitList(self, Ahead, Dhead): 
+        ascn = Ahead 
+        dscn = Dhead 
+        curr = self.head 
+        # Link alternate nodes 
+        while curr != None: 
+            # Link alternate nodes in ascending order 
+            ascn.next = curr 
+            ascn = ascn.next
+            curr = curr.next
+            if curr != None: 
+                dscn.next = curr 
+                dscn = dscn.next
+                curr = curr.next
+        ascn.next = None
+        dscn.next = None
+
+# Driver program 
+llist = LinkedList() 
+llist.head = llist.newNode(10) 
+llist.head.next  = llist.newNode(40) 
+llist.head.next.next = llist.newNode(53) 
+llist.head.next.next.next = llist.newNode(30) 
+llist.head.next.next.next.next = llist.newNode(67) 
+llist.head.next.next.next.next.next = llist.newNode(12) 
+llist.head.next.next.next.next.next.next = llist.newNode(89) 
+
+print 'Given linked list'
+llist.printList() 
+
+llist.sort() 
+
+print 'Sorted linked list'
+llist.printList()