package algorithms;

/**

* 206. Reverse Linked List

* https://leetcode.com/problems/reverse-linked-list/

* Difficulty : Easy

* Related Topics : Linked List

*

* 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

*

* created by cenkc on 5/10/2021

*/

public class ReverseLinkedList {

public ListNode reverseList(ListNode head) {

if (head == null) {

return null;

}

ListNode previous = null;

while (head != null) {

ListNode next = head.next;

head.next = previous;

previous = head;

head = next;

}

return previous;

}

private class ListNode {

int val;

ListNode next;

ListNode() {

}

ListNode(int val) {

this.val = val;

}

ListNode(int val, ListNode next) {

this.val = val;

this.next = next;

}

}

}