leetcode - 92.Reverse Linked List II

Reverse Linked List II

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

For example:

Given

1->2->3->4->5->NULL

, m =

2

and n =

4

,

return

1->4->3->2->5->NULL

.

Note:

Given m, n satisfy the following condition:

1 ≤ m ≤ n ≤ length of list.

Solution:

public ListNode reverseBetween(ListNode head, int m, int n) {
if (head == null)
return null;
ListNode root = new ListNode(0);
root.next = head;
ListNode pre = root;
for (int i = 0; i < m - 1; i++)
pre = pre.next;

ListNode start = pre.next;
ListNode then = start.next;

for (int i = 0; i < n - m; i++) {
start.next = then.next;
then.next = pre.next;
pre.next = then;
then = start.next;
}

return root.next;
}