Find Loop

• Time : O(n)
• Space : O(1)

#include <vector>
using namespace std;

class LinkedList {
public:
    int value;
    LinkedList *next;

    LinkedList(int value);
};

LinkedList *findLoop(LinkedList *head) {
    LinkedList *slow = head, *fast = head;
    do {
        slow = slow->next;
        fast = fast->next->next;
    }while(slow != fast);
    
    while(head != slow) {
        slow = slow->next;
        head = head->next;
    }
    return head;
}