Free AI LeetCode Communication Coach — Climbing Stairs

The problem

You can climb 1 or 2 steps. How many distinct ways to climb n stairs?

Example: n = 3 → 3 (1+1+1, 1+2, 2+1)

Recurrence first, then rolling vars.

if n <= 2:
    return n
a, b = 1, 2
for _ in range(3, n + 1):
    a, b = b, a + b
return b

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 …”

• “Ways(n) is ways(n-1) plus ways(n-2).”
• “I keep only the last two values.”

Practise out loud

1. 1. Restate

   I need the number of ways to reach the top taking one or two steps at a time.

2. 2. Approach

   This is Fibonacci. Ways to reach n equal ways to n−1 plus ways to n−2. I compute bottom-up with two variables.

3. 3. Example

   For n = 3 the ways are three: 1+1+1, 1+2, and 2+1.

4. 4. Time and space

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

5. 5. Edge cases

   I would check n equals one and n equals two as base cases.

Common mistakes when explaining Climbing Stairs

• Jumping to the formula without the recurrence story.
• Saying O(n) space when two variables suffice.