moonlightshadow123
5/30/2017 - 2:28 PM

24. Swap Nodes in Pairs

  1. Swap Nodes in Pairs
# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def swapPairs(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        dummy = ListNode(0)
        dummy.next = head
        dummy.next = self.recursive(head)
        return dummy.next
    def recursive(self, node):
        if node == None or node.next == None:
            return node
        p = node.next
        node.next = self.recursive(p.next)
        p.next = node
        return p

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def swapPairs(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        dummy = ListNode(0)
        dummy.next = head
        prev = dummy
        p = dummy.next
        while p != None and p.next != None:
            n = p.next
            nn = n.next
            prev.next = n
            n.next = p
            p.next = nn
            prev = p
            p = nn
        return dummy.next

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.