Reverse Linked List

Problem

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

Follow up:

A linked list can be reversed either iteratively or recursively. Could you implement both?

Code

C++ 1

class Solution {
public:
    ListNode* reverseList(ListNode* head) {

        ListNode* reverseList(ListNode* head) {
        ListNode *nextNode, *prevNode = NULL;
        while (head) {
            nextNode = head->next;
            head->next = prevNode;
            prevNode = head;
            head = nextNode;
        }
        return prevNode;
    }
};

C++ 2

class Solution {
public:
    ListNode* reverseList(ListNode *head, ListNode *nextNode = NULL, ListNode *prevNode = NULL) {
        return head ? reverseList(head->next, (head->next = prevNode, nextNode), head) : prevNode;
    }
};

Reference

[1] https://leetcode.com/problems/reverse-linked-list/solutions/803955/c-iterative-vs-recursive-solutions-compared-and-explained-99-time-85-space/
[2] https://leetcode.com/problems/reverse-linked-list/solutions/3211778/using-2-methods-iterative-recursive-beats-97-91/