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/**
 * 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) {

        cin.tie(nullptr)->sync_with_stdio(0);
        
        ListNode* preNode = nullptr;

        while (head != nullptr) {
            ListNode* tempNode = head->next;
            head->next = preNode;
            preNode = head;
            head = tempNode;
        }

        return preNode;
    }
};