code.cpp

/* **************************************************************************
 * Copyright 2024 The OpenGenus.org Authors. All Rights Reserved.
 *
 * Code for the book "DAILY 43: Algorithmic Problems for Coding Interviews: Easy level, C++ edition"
 *
 * Licensed under the GNU General Public License, Version 3.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.gnu.org/licenses/gpl-3.0.html
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * For details about the book, please visit: https://www.amazon.com/dp/B0CZJNBLQS
 * *************************************************************************/

#include <iostream>

class ListNode {
public:
    int val;
    ListNode* next;
    ListNode(int val) : val(val), next(nullptr) {}
};

bool hasCycle(ListNode* head) {
    ListNode* fast = head;
    ListNode* slow = head;
    while (fast != nullptr && fast->next != nullptr) {
        fast = fast->next->next;
        slow = slow->next;
        if (fast == slow)
            return true;
    }
    return false;
}

int main() {
    ListNode* head = new ListNode(1);
    head->next = new ListNode(2);
    head->next->next = new ListNode(3);
    head->next->next->next = new ListNode(4);
    head->next->next->next->next = head->next; // Creating a cycle

    bool hasCycleResult = hasCycle(head);
    if (hasCycleResult) {
        std::cout << "The linked list has a cycle." << std::endl;
    } else {
        std::cout << "The linked list does not have a cycle." << std::endl;
    }

    return 0;
}