D66_Detect Loop in linked list.cpp

// You are given the head of a singly linked list. Your task is to determine if the linked list contains a loop. A loop exists in a linked list if the next pointer of the last node points to any other node in the list (including itself), rather than being null.

// Custom Input format:
// A head of a singly linked list and a pos (1-based index) which denotes the position of the node to which the last node points to. If pos = 0, it means the last node points to null, indicating there is no loop.

// Examples:

// Input: head: 1 -> 3 -> 4, pos = 2
// Output: true
// Explanation: There exists a loop as last node is connected back to the second node.

class Solution
{
public:
    // Function to check if the linked list has a loop.
    bool detectLoop(Node *head)
    {
        // your code here
        if (head == nullptr)
            return false;

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