Python Program For Swapping Nodes In A Linked List Without Swapping Data

# Python program to swap two given nodes 
# of a linked list
class LinkedList(object):
    def __init__(self):
        self.head = None

    # Head of list
    class Node(object):
        def __init__(self, d):
            self.data = d
            self.next = None

    # Function to swap Nodes x and y 
    # in a linked list by changing links
    def swapNodes(self, x, y):

        # Nothing to do if x and y are
        # the same
        if x == y:
            return

        # Search for x (keep track of 
        # prevX and CurrX)
        prevX = None
        currX = self.head
        while currX != None and currX.data != x:
            prevX = currX
            currX = currX.next

        # Search for y (keep track of 
        # prevY and currY)
        prevY = None
        currY = self.head
        while currY != None and currY.data != y:
            prevY = currY
            currY = currY.next

        # If either x or y is not present, 
        # nothing to do
        if currX == None or currY == None:
            return

        # If x is not head of linked list
        if prevX != None:
            prevX.next = currY

        else:  # make y the new head
            self.head = currY

        # If y is not head of linked list
        if prevY != None:
            prevY.next = currX
        else:  

            # make x the new head
            self.head = currX

        # Swap next pointers
        temp = currX.next
        currX.next = currY.next
        currY.next = temp

    # Function to add Node at beginning
    # of list.
    def push(self, new_data):

        # 1. alloc the Node and put the data
        new_Node = self.Node(new_data)

        # 2. Make next of new Node as head
        new_Node.next = self.head

        # 3. Move the head to point to new Node
        self.head = new_Node

    # This function prints contents of 
    # linked list starting from the given Node
    def printList(self):
        tNode = self.head
        while tNode != None:
            print tNode.data,
            tNode = tNode.next

# Driver code
llist = LinkedList()

# The constructed linked list is:
# 1->2->3->4->5->6->7
llist.push(7)
llist.push(6)
llist.push(5)
llist.push(4)
llist.push(3)
llist.push(2)
llist.push(1)
print "Linked list before calling swapNodes() "
llist.printList()
llist.swapNodes(4, 3)
print "
Linked list after calling swapNodes() "
llist.printList()
# This code is contributed by BHAVYA JAIN

# Python3 program to swap two given
# nodes of a linked list

# A linked list node class
class Node:

    # constructor
    def __init__(self, val = None, 
                 next1 = None):
        self.data = val
        self.next = next1

    # Print list from this
    # to last till None
    def printList(self):
        node = self

        while (node != None):
            print(node.data, end = " ")
            node = node.next
        print(" ")

# Function to add a node
# at the beginning of List
def push(head_ref, new_data):

    # Allocate node
    (head_ref) = Node(new_data, head_ref)
    return head_ref

def swapNodes(head_ref, x, y):
    head = head_ref

    # Nothing to do if x and y are same
    if (x == y):
        return None

    a = None
    b = None

    # Search for x and y in the linked list
    # and store their pointer in a and b
    while (head_ref.next != None):

        if ((head_ref.next).data == x):
            a = head_ref

        elif ((head_ref.next).data == y):
            b = head_ref

        head_ref = ((head_ref).next)

    # If we have found both a and b
    # in the linked list swap current
    # pointer and next pointer of these
    if (a != None and b != None):
        temp = a.next
        a.next = b.next
        b.next = temp
        temp = a.next.next
        a.next.next = b.next.next
        b.next.next = temp

    return head

# Driver code
start = None

# The constructed linked list is:
# 1.2.3.4.5.6.7
start = push(start, 7)
start = push(start, 6)
start = push(start, 5)
start = push(start, 4)
start = push(start, 3)
start = push(start, 2)
start = push(start, 1)

print("Linked list before calling swapNodes() ")
start.printList()
start = swapNodes(start, 6, 1)
print("Linked list after calling swapNodes() ")
start.printList()
# This code is contributed by Arnab Kundu