206. Reverse Linked List.java

/*
Given the head of a singly linked list, reverse the list, and return the reversed list.

 

Example 1:


Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]
Example 2:


Input: head = [1,2]
Output: [2,1]
Example 3:

Input: head = []
Output: []
 

Constraints:

The number of nodes in the list is the range [0, 5000].
-5000 <= Node.val <= 5000
*/



//Solution
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        if(head == null || head.next == null){
            return head;
        }
        ListNode temp = reverseList(head.next);
        ListNode node = head.next;
        node.next = head;
        head.next = null;
        return temp;
    }
}