Clarify that the problem reduces to finding the maximum frequency of any digit (0-9) across all numbers, since a subset sharing a common digit must all contain that digit. Iterate through each number, extract its digits, and count occurrences per digit; the answer is the maximum count. This yields an O(n) time and O(1) space solution.
Pro tip: Mention that the problem is equivalent to finding the most frequent digit, and note that the two-digit constraint (10-99) ensures no leading zeros, simplifying digit extraction. This shows you can simplify the problem and handle edge cases.
Confirm that the subset must share at least one common digit, and that the subset can be any size. Ask if the array can be empty or contain duplicates.
Realize that the largest subset sharing a common digit is simply the set of all numbers containing the most frequent digit. So the problem reduces to finding the maximum frequency of any digit.
Use an array of size 10 to count occurrences of each digit. For each number, extract its tens and ones digits, increment their counts, and track the maximum.
State that the algorithm runs in O(n) time and O(1) space, which is optimal. Mention that each number is processed once.
Walk through a small example, such as [12, 23, 34, 45], to verify the approach. Also consider edge cases like all numbers sharing a digit or no common digit.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.