206.reverse-linked-list.java

/*
 * @lc app=leetcode id=206 lang=java
 *
 * [206] Reverse Linked List
 *
 * https://leetcode.com/problems/reverse-linked-list/description/
 *
 * algorithms
 * Easy (55.02%)
 * Likes:    2405
 * Dislikes: 64
 * Total Accepted:    608.3K
 * Total Submissions: 1.1M
 * 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) {
        ListNode prev = null;
        ListNode curr = head;
        while (curr != null) {
            ListNode tempNext = curr.next;
            curr.next = prev;
            prev = curr;
            curr = tempNext;
        }
        return prev;
    }
}