Find largest subset sharing a common digit

Q: Find largest subset sharing a common digit

This question evaluates the ability to analyze arrays for the largest subset sharing a common digit, emphasizing digit-level feature extraction, frequency analysis, and set-based reasoning. Commonly asked in the Coding & Algorithms domain, it assesses practical algorithmic implementation and efficient aggregation/counting with basic data structures rather than purely conceptual reasoning.

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Question

You are given a list A of two-digit integers (each from 10 to 99). Two integers are said to “share a digit” if they have at least one digit in common (e.g., 23 and 35 share digit 3).

Determine the maximum size of a subset of A such that all numbers in the subset share at least one common digit (i.e., there exists a digit d in {0,1,...,9} that appears in every number in the chosen subset).

Input: Array/list A of length m, with each A[i] in [10, 99].

Output: An integer = the maximum possible subset size.

Example:

A = [23, 35, 30, 19]
The digit 3 appears in 23, 35, 30 → answer is 3 .

Find largest subset sharing a common digit

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