206.reverse-linked-list.cpp

/*
 * @lc app=leetcode id=206 lang=cpp
 *
 * [206] Reverse Linked List
 */

// @lc code=start
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
  public:
    ListNode* reverseList(ListNode* head) {
        if (head == nullptr || head->next == nullptr) return head;
        ListNode *next = head, *current = head->next, *prev = current->next;
        next->next = nullptr;
        while (prev) {
            current->next = next;
            next = current;
            current = prev;
            prev = prev->next;
        }
        current->next = next;

        return current;
    }
};
// @lc code=end