Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list’s nodes (i.e., only nodes themselves may be changed.)
Example 1:
Input: head = [1,2,3,4] Output: [2,1,4,3]
- code
class Solution:
def swapPairs(self, head):
res = pre = ListNode()
pre.next = head
while pre.next and pre.next.next:
first = pre.next
second = pre.next.next
pre.next, second.next, first.next = second, first, second.next
# pre = a
pre = pre.next.next
return res.next
- code
class Solution:
def swapPairs(self, head: ListNode) -> ListNode:
if not head or not head.next:
return head
def helper(node):
if not node or not node.next:
return node
rest = node.next.next
nexNode = node.next
node.next.next = node
node.next = helper(rest)
return nexNode
return helper(head)