[leetcode 92] Reverse Linked List II

LeetCode-92

Reverse Linked List II : Given the head of a singly linked list and two integers left and right where left <= right, reverse the nodes of the list from position left to position right, and return the reversed list.

note : 1 <= left <= right <= n

Answer

        :::python

# Definition for singly-linked list.
# class ListNode:
#     def init(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reverseBetween(self, head: Optional[ListNode], left: int, right: int) -> Optional[ListNode]:
        if not head or left == right:
            return head
        root = start = ListNode(None)
        root.next = head
        for _ in range(left-1):
            start = start.next
        end = start.next
        for _ in range(right-left):
            tmp, start.next, end.next = start.next, end.next, end.next.next
            start.next.next = tmp
        return root.next

Result : 34ms Memory: 13.9mb