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o(n) time and o(1) space using two pointers.
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1721. Swapping Nodes in a Linked List/1721. Swapping Nodes in a Linked List.py
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""" | ||
You are given the head of a linked list, and an integer k. | ||
Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). | ||
Example 1: | ||
Input: head = [1,2,3,4,5], k = 2 | ||
Output: [1,4,3,2,5] | ||
Example 2: | ||
Input: head = [7,9,6,6,7,8,3,0,9,5], k = 5 | ||
Output: [7,9,6,6,8,7,3,0,9,5] | ||
Constraints: | ||
The number of nodes in the list is n. | ||
1 <= k <= n <= 105 | ||
0 <= Node.val <= 100 | ||
""" | ||
# Definition for singly-linked list. | ||
# class ListNode: | ||
# def __init__(self, val=0, next=None): | ||
# self.val = val | ||
# self.next = next | ||
class Solution: | ||
def swapNodes(self, head: Optional[ListNode], k: int) -> Optional[ListNode]: | ||
left,right = head,head | ||
for _ in range(k-1): | ||
right = right.next | ||
r = right | ||
while right.next: | ||
left = left.next | ||
right = right.next | ||
r.val,left.val = left.val,r.val | ||
return head |