[leetcode] 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.

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

 

思路：链表操作。

public class Solution {
    public ListNode reverseBetween(ListNode head, int m, int n) {
        ListNode newHead = new ListNode(-1);
        newHead.next = head;
        ListNode p = newHead;
        for (int i = 0; i < m - 1; i++) {
            p = p.next;
        }
        ListNode pre = p;
        ListNode start = p.next;

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

        }

        return newHead.next;
    }

    public static void main(String[] args) {
        ListNode head = ListUtils.makeList(new int[] { 1, 2, 3, 4, 5 });
        ListUtils.printList(head);
        head = new Solution().reverseBetween(head, 4, 5);
        ListUtils.printList(head);
    }

}

 

第二遍记录：

reverse链表的方法，每次添加在pre的后面。