Today I have done leetcode's March LeetCoding Challenge with cpp.

March LeetCoding Challenge 21

Description

Reverse 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

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

Solution

class Solution {
public:
  ListNode* reverseList(ListNode* head, ListNode* tail = nullptr) {
    if(!head) return tail;
    ListNode *next = head->next;
    head->next = tail;
    return reverseList(next, head);
  }
};

// Accepted
// 28/28 cases passed (4 ms)
// Your runtime beats 96.22 % of cpp submissions
// Your memory usage beats 97.51 % of cpp submissions (8.2 MB)