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Capital One·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Capital One SWE interview with a coding problem around digit counting. Pretty straightforward premise but the edge cases are where it gets you.

Questions Asked (1)

Q1

Given an array of non-negative integers, count how many of them contain an odd number of the digit '0' in their decimal representation. The number 0 itself counts as having one zero digit.

Algorithms & Data Structures
Author's notes

Spent the first minute overcomplicating it in my head.

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AI HintsAI Generated

Suggested Approach

Clarify edge cases like zero and leading zeros, then iterate through the array, converting each number to a string and counting the occurrences of '0'. If the count is odd, increment a counter. Return the final count.

Pro tip: Mention that you can avoid string conversion by using arithmetic (repeated modulo and division) to count zeros, which is more efficient and shows deeper understanding. Also, explicitly handle the special case of 0 as stated.

1. Clarify the problem

Confirm that numbers are non-negative, that 0 counts as having one zero, and that leading zeros are not considered (e.g., 5 is '5', not '05').

2. Choose a method to count zeros

Decide between string conversion or arithmetic. String conversion is simpler; arithmetic avoids type conversion overhead.

3. Iterate and count

Loop through each number, count the zeros in its decimal representation, and if the count is odd, increment a result counter.

4. Handle edge cases

Ensure that 0 is correctly counted as having one zero. Also consider very large numbers if using arithmetic.

5. Return the result

After processing all numbers, return the total count of numbers with an odd number of zeros.

Key Points to Mention

  • Time complexity: O(n * d) where n is the number of elements and d is the average number of digits.
  • Space complexity: O(1) extra space if using arithmetic, O(d) if using string conversion per number.
  • Edge case: 0 has exactly one zero, so it should be counted.
  • Leading zeros are not considered in the decimal representation of a number.
  • Alternative approaches: string conversion vs. arithmetic (modulo/division).
  • Potential optimization: early termination if counting zeros exceeds a threshold? Not needed for odd count.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.