Section 1Understand Problem
Section 01
Understand the problem
Restate the problem precisely. Interviewers reward candidates who pause, define the contract, and name the guarantees before coding.
Problem statement
A message containing letters from A-Z can be encoded into numbers using the mapping 'A'→"1", 'B'→"2", …, 'Z'→"26". To decode an encoded message, all the digits must be grouped, then mapped back into letters using the reverse of the mapping. Note that '06' is **not** a valid encoding of 'F'. Given a string `s` containing only digits, return the number of ways to decode it. The answer is guaranteed to fit in a 32-bit integer.
Example
s = "12" → 2
Constraints
1 ≤ s.length ≤ 100 · s contains only digits and may contain leading zero(s)
Audio recording unsupported on this browser.
WPM—Fillers0Pace—Thinking0%
Explain the problem in your own words
0 words0 chars
AI Review
Write your thinking above first.
Once you've drafted a response, click Submit for AI review and a senior engineer will critique your reasoning.
Ready to submit Section 1?
The reviewer will check whether you stated inputs, output, guarantees, and any assumption you flagged.
Write at least a couple of sentences explaining the problem before submitting.