92. Reverse Linked List II

Reverse a linked list from position m to n. Do it in one-pass.

Note: 1 ≤ m ≤ n ≤ length of list.

Example:

Input: 1->2->3->4->5->NULL, m = 2, n = 4
Output: 1->4->3->2->5->NULL

Code:

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

class Solution(object):
    def reverseBetween(self, head, m, n):
        dummy = ListNode(0)
        dummy.next = head
        
        cur, prev = head, dummy
        for _ in range(m - 1):
            cur = cur.next
            prev = prev.next
        
        for _ in range(n - m):
            temp = cur.next
            cur.next = temp.next
            temp.next = prev.next
            prev.next = temp

        return dummy.next