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Bloomberg·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Bloomberg SWE interview, got hit with a classic palindrome number problem. Pretty standard stuff, nothing that'll make your jaw drop.

Questions Asked (1)

Q1

Determine whether a given integer is a palindrome without converting it to a string.

Algorithms & Data Structures
Author's notes

Classic problem, you've probably seen it a hundred times.

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AI HintsAI Generated

Suggested Approach

Clarify edge cases like negative numbers and numbers ending in zero, then reverse only half of the integer to avoid overflow and achieve O(log n) time. Compare the reversed half with the remaining half, handling odd digit counts by ignoring the middle digit.

Pro tip: Mention that reversing only half the number prevents integer overflow and is more efficient; also note that negative numbers are not palindromes by definition, and numbers ending in zero (except zero itself) cannot be palindromes.

1. Clarify constraints and edge cases

Ask about input range, negative numbers, and numbers ending in zero. State that negative numbers are not palindromes and that any positive number ending in zero (except 0) cannot be a palindrome.

2. Handle trivial cases

Immediately return false for negative numbers and for numbers that end in zero but are not zero. Return true for single-digit numbers.

3. Reverse half the number

Iteratively extract the last digit of the original number and build the reversed half. Stop when the reversed half is greater than or equal to the remaining original half.

4. Compare halves

Check if the reversed half equals the remaining original half (for even digit counts) or if the reversed half divided by 10 equals the remaining half (for odd digit counts).

5. Analyze complexity and test

State that time complexity is O(log n) and space is O(1). Walk through examples like 121, 1221, 12321, 10, and -121 to verify correctness.

Key Points to Mention

  • Negative numbers are not palindromes (e.g., -121 reversed is 121-, which is invalid).
  • Numbers ending in zero (except 0) cannot be palindromes because the reversed number would have a leading zero.
  • Reversing only half the integer avoids integer overflow and reduces the number of operations.
  • Time complexity is O(log n) because we process each digit once; space complexity is O(1).
  • Handling odd digit counts by ignoring the middle digit (e.g., compare reversedHalf/10 with remainingHalf).
  • Edge cases: 0 is a palindrome, single-digit numbers are palindromes.

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