LLcycle.md

141. Linked List Cycle, Easy

• a Must know problem
• Idea is to use two pointer, one is slow and one is fast.
• Traverse them, one with normal rate, other one with twice the rate,
• If they match somewhere then there must be cycle, else not.

Code

   bool hasCycle(ListNode *head) {
        if (!head) return false;
        auto s = head; 
        auto f = head;
        
        while (f -> next and f -> next -> next) {
            s = s -> next;
            f = f -> next -> next;
            
            if (s == f) return true;
        }
        return false;
        
    }