Linked List Cycle - ELI5 Park

👶 The 5-Year-Old Summary

You're in a treasure hunt room. Some treasure hunts end at "null" (no more clues), but some loops back to a previous room! Detect if you're stuck in a loop!

🎮 Interactive Visualizer

Floyd's Tortoise & Hare Algorithm!

List: 3 → 2 → 0 → -4 → (back to 2)

🐢 Slow (1 step)

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🐇 Fast (2 steps)

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🧠 The Brain Hack

Floyd's Cycle Detection! Use two pointers - slow moves 1 step, fast moves 2 steps. If there's a cycle, they MUST meet! It's like two runners on a circular track!

💻 The Clean Solution

def has_cycle(head):
    if not head or not head.next:
        return False
    
    # Start at head
    slow = head
    fast = head
    
    # Move slow by 1, fast by 2
    while fast and fast.next:
        slow = slow.next
        fast = fast.next.next
        
        # They met = cycle exists!
        if slow == fast:
            return True
    
    # Fast reached end = no cycle
    return False

Time: O(n)

Space: O(1)