C++: Iterative

1class Solution {
2  public:
3    ListNode* reverseList(ListNode* head) {
4      ListNode *prev = nullptr;
5      ListNode *curr = head;
6
7      while (curr != nullptr) {
8        ListNode *temp = curr->next;
9        curr->next = prev;
10        prev = curr;
11        curr = temp;
12      }
13
14      return prev;
15    }
16};

C++: Recursion

1class Solution {
2  public:
3    ListNode* reverseList(ListNode* head) {
4      if (head == nullptr || head->next == nullptr) return head;
5
6      ListNode *p = reverseList(head->next);
7      head->next->next = head;
8      head->next = nullptr;
9      return p;
10    }
11};

JavaScript: Iterative

1var reverseList = function(head) {
2  let prev = null;
3  let curr = head;
4
5  while(curr != null) {
6    let temp = curr.next;
7    curr.next = prev;
8    prev = curr;
9    curr = temp;
10  }
11
12  return prev;
13};

JavaScript: Recursion

1var reverseList = function(head) {
2  if (head == null || head.next == null) return head;
3
4  let p = reverseList(head.next);
5  head.next.next = head;
6  head.next = null;
7  return p;
8};

Ruby: Iterative

1def reverse_list(head)
2  prev = nil
3  curr = head
4
5  while(curr != nil) do
6    temp = curr.next
7    curr.next = prev
8    prev = curr
9    curr = temp
10  end
11
12  return prev
13end

Ruby: Recursion

1def reverse_list(head)
2  return head if head==nil or head.next==nil
3
4  p = reverse_list(head.next)
5  head.next.next = head
6  head.next = nil
7  p
8end