#include <iostream>
#include <memory>

struct ListNode {
    int val;
    std::shared_ptr<ListNode> next;
    ListNode(int x) : val(x), next(nullptr) {}
};

bool hasCycle(std::shared_ptr<ListNode> head) {
    auto slow = head;
    auto fast = head;

    while (fast != nullptr && fast->next != nullptr) {
        slow = slow->next;
        fast = fast->next->next;

        if (slow == fast) {
            return true;
        }
    }

    return false;
}

int main() {
    auto head = std::make_shared<ListNode>(1);
    head->next = std::make_shared<ListNode>(2);
    head->next->next = std::make_shared<ListNode>(3);
    head->next->next->next = std::make_shared<ListNode>(4);
    head->next->next->next->next = head->next;

    std::cout << hasCycle(head) << std::endl; // Output: 1 (true)

    return 0;
}