206. Reverse Linked List

• Difficulty: Easy

• Topics: Linked List

• Similar Questions:

  • Reverse Linked List II

  • Binary Tree Upside Down

  • Palindrome Linked List

Problem:

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?

Solutions:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if (head == NULL || head->next == NULL) return head;
        ListNode* reverseSubList = reverseList(head->next);
        head->next->next = head;
        head->next = NULL;
        return reverseSubList;
    }
};