Find largest subset sharing a common digit
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
You are given a list of **two-digit integers** (each from `10` to `99`, inclusive). You want to select as many numbers as possible **in one selection** such that:
- There exists a digit `d` (0–9) where **every selected number contains digit `d` in at least one position** (tens or ones).
For example, from `[11, 21, 31, 41, 16, 17, 18, 34, 57]`, you can select `11, 21, 31, 41, 16, 17, 18` (7 numbers) because they all contain digit `1`.
Return the **maximum possible size** of such a selection.
### Input
- An integer array `nums` of length `n`, where each `nums[i]` is a two-digit integer (`10`–`99`).
### Output
- An integer: the maximum number of elements you can select.
Overview: This question evaluates understanding of digit-level properties within arrays and the ability to reason about selection size under explicit constraints, involving combinatorial and counting concepts.
Read the full Google Software Engineer interview experience this question came from
Given two-digit integers, return the largest number of elements that all contain one common digit.
Constraints
- Numbers are two-digit integers in normal inputs
Examples
Input: ([11, 21, 31, 41, 16, 17, 18, 34, 57],)
Expected Output: 7
Input: ([23, 35, 30, 19],)
Expected Output: 3
Hints
- Count how many numbers contain each digit, counting a number once per digit even if repeated.