algorithms/algorithms/linkedlist/swap_in_pairs.py at master · monsterofhell/algorithms

30 lines (27 loc) · 759 Bytes

"""

Given a linked list, swap every two adjacent nodes

and return its head.

For example,

Given 1->2->3->4, you should return the list as 2->1->4->3.

Your algorithm should use only constant space.

You may not modify the values in the list,

only nodes itself can be changed.

"""

class Node(object):

def __init__(self, x):

self.val = x

self.next = None

def swap_pairs(head):

if not head:

return head

start = Node(0)

start.next = head

current = start

while current.next and current.next.next:

first = current.next

second = current.next.next

first.next = second.next

current.next = second

current.next.next = first

current = current.next.next

return start.next

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