My first instinct was to brute-force every possible digit 0-9, count how many numbers in the list contain that digit, then return the max.
Clarify that each number is two-digit and we need the largest subset sharing at least one common digit. Since digits are only 0-9, count how many numbers contain each digit and return the maximum count. Mention that this is O(n) time and O(1) space.
Pro tip: Proactively discuss edge cases like numbers with repeated digits (e.g., 11) and leading zeros (e.g., 05), and confirm whether the list can be empty or contain non-two-digit numbers.
Confirm that 'share at least one digit' means any common digit, and that numbers are exactly two-digit. Ask about input size, duplicates, and edge cases.
Recognize that the common digit must be one of the 10 possible digits (0-9). Therefore, the maximum subset size is the maximum frequency of any digit across all numbers.
Initialize an array of size 10 to count digit occurrences. For each number, extract its two digits and increment the counts for each distinct digit.
State that the algorithm runs in O(n) time and O(1) space, since the digit count array is fixed size.
Discuss handling of numbers with repeated digits (count once per number), leading zeros, empty input, and potential duplicates.
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