Leetcode 92. Reverse Linked List II

https://leetcode.com/problems/reverse-linked-list-ii/

Simple problem. If you know how to reverse a linked list, this problem will not be very hard.

Solution:

# T:O(n) S:O(1)
class Solution:
    # @param head, a ListNode
    # @param m, an integer
    # @param n, an integer
    # @return a ListNode
    def reverseBetween(self, head, m, n):
        if head == None or head.next == None:
            return head
        dummy = ListNode(0) 
        dummy.next = head
        head1 = dummy
        for i in range(m - 1):
            head1 = head1.next
        p = head1.next
        for i in range(n - m):
            tmp = head1.next
            head1.next = p.next
            p.next = p.next.next
            head1.next.next = tmp
        return dummy.next

Run Time: 64 ms