206.reverse-linked-list.1.java

/*
 * @lc app=leetcode id=206 lang=java
 *
 * [206] Reverse Linked List
 *
 * https://leetcode.com/problems/reverse-linked-list/description/
 *
 * algorithms
 * Easy (52.81%)
 * Total Accepted:    520.1K
 * Total Submissions: 984.7K
 * Testcase Example:  '[1,2,3,4,5]'
 *
 * Reverse a singly linked list.
 *
 * Example:
 *
 *
 * Input: 1->2->3->4->5->NULL
 * Output: 5->4->3->2->1->NULL
 *
 *
 * Follow up:
 *
 * A linked list can be reversed either iteratively or recursively. Could you
 * implement both?
 *
 */
/**
 * Definition for singly-linked list. public class ListNode { int val; ListNode
 * next; ListNode(int x) { val = x; } }
 */
class Solution {
  public ListNode reverseList(ListNode head) {
    if (head == null || head.next == null) {
      return head;
    }

    ListNode node = reverseList(head.next);
    head.next.next = head;
    head.next = null;
    return node;
  }
}