Bloomberg·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026

Summary

Bloomberg SWE coding round, just the one question about string frequency cleanup. Pretty straightforward premise but the edge cases are where it gets you.

Questions Asked (1)

Given a string, find the minimum number of character deletions required so that every character in the string has a unique frequency.

Algorithms & Data Structures

Author's notes

The naive approach feels obvious until you start thinking about what happens when multiple characters collide on the same count.

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AI HintsAI Generated

Suggested Approach

Count the frequency of each character, then greedily adjust frequencies to be unique by reducing duplicates and resolving collisions. Use a set to track used frequencies and a max-heap or sorted list to process frequencies in descending order, ensuring minimal deletions.

Pro tip: After solving, discuss how the greedy choice of reducing the highest duplicate frequency minimizes deletions, and mention that the problem can be solved in O(n + k log k) time where k is the number of distinct characters.

1. Count Frequencies

Traverse the string and count the frequency of each character using a hash map or array.

2. Sort Frequencies

Extract the frequency values and sort them in descending order to handle the largest frequencies first.

3. Greedy Adjustment

Iterate through sorted frequencies, and for each, if it's already used, decrement it until it's unique or zero, counting deletions.

4. Track Used Frequencies

Use a set to keep track of frequencies that have been assigned to ensure uniqueness.

5. Return Deletions

Sum the total deletions made and return that as the minimum number.

Key Points to Mention

Frequency counting using hash map or array
Greedy strategy: reduce highest frequencies first to minimize deletions
Use of a set to detect and avoid duplicate frequencies
Time complexity: O(n + k log k) where k is number of distinct characters
Space complexity: O(k) for frequency map and set
Edge cases: empty string, all characters same, already unique frequencies

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