92 Reverse Linked List II

92. Reverse Linked List II

1. Question

Reverse a linked list from positionmton. Do it in-place and in one-pass.

For example: Given1->2->3->4->5->NULL,m= 2 andn= 4,

return1->4->3->2->5->NULL.

Note: Givenm,nsatisfy the following condition: 1 ≤m≤n≤ length of list.

2. Implementation

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode reverseBetween(ListNode head, int m, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;

        ListNode preNode = dummy;

        for (int i = 1; i <= m - 1; i++) {
            preNode = preNode.next;
        }

        ListNode curNode = preNode.next;
        ListNode nextNode = curNode.next;

        for (int i = m; i < n; i++) {
            curNode.next = nextNode.next;
            nextNode.next = preNode.next;
            preNode.next = nextNode;
            nextNode = curNode.next;
        }
        return dummy.next;
    }
}

3. Time & Space Complexity

时间复杂度O(m - n + 1), 空间复杂度O(1)