Free AI LeetCode Communication Coach — Linked List Cycle

The problem

Given head, return true if the linked list has a cycle.

Example: list with a cycle back to an earlier node → true

Name tortoise and hare.

slow = fast = head
while fast and fast.next:
    slow = slow.next
    fast = fast.next.next
    if slow is fast:
        return True
return False

How to explain it

1. 1. Restate

   Say the problem in your own words.

   One or two sentences. Show you understood the input, the output, and the goal — not that you memorised the prompt.

2. 2. Approach

   Name the method before you code.

   Brute force first if you need it, then the structure you will use: hash map, two pointers, stack, binary search.

3. 3. Example

   Walk one concrete input.

   Pick small numbers. Say what you store, what you compare, and what you return. Interviewers follow an example more easily than abstract talk.

4. 4. Time and space

   One sentence each.

   After the example, before you claim you are done. “Time is O(n) because we scan once. Space is O(n) for the map.”

5. 5. Edge cases

   Name at least one unusual input.

   Empty input, duplicates, already sorted, overflow. Invite a follow-up: “I would also check …”

• “Slow moves one, fast moves two.”
• “If they meet, there is a cycle.”

Practise out loud

1. 1. Restate

   I need to know if following next pointers can loop forever.

2. 2. Approach

   I use two pointers. Slow moves one step, fast moves two. If they meet, there is a cycle. If fast hits null, there is not.

3. 3. Example

   If a node points back earlier, fast laps slow inside the loop and they collide.

4. 4. Time and space

   Time is O(n). Space is O(1).

5. 5. Edge cases

   I would check null head and a single node with no self-loop.

Common mistakes when explaining Linked List Cycle

• Not explaining why meeting implies a cycle.
• Null-checking only slow, not fast.next.