DoorDash·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

DoorDash coding screen, one question the whole time. Pretty focused session, nothing too wild, but the problem had a small wrinkle that tripped me up for a minute before I got back on track.

Questions Asked (1)

Given two equal-length strings and an integer k, determine if you can make the first string an anagram of the second by changing at most k characters.

Algorithms & Data Structures

Author's notes

I knew frequency counting was the right move but fumbled the aggregation step.

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AI HintsAI Generated

Suggested Approach

Clarify that 'changing at most k characters' means you can replace characters in the first string to make it an anagram of the second. Use frequency counting: compute the difference in character counts between the two strings, and the minimum number of changes needed is the sum of positive differences (or half the sum of absolute differences). Compare this minimum to k.

Pro tip: Mention that the problem reduces to counting mismatched characters after accounting for duplicates, and note that the minimum changes equals the number of characters in the first string that are not matched in the second. This shows you understand the underlying combinatorial optimization.

1. Clarify the problem

Confirm that 'changing' means replacing a character in the first string, and that the goal is to make the first string an anagram of the second. Also confirm that strings are equal length and contain only lowercase English letters (or clarify character set).

2. Count character frequencies

Build frequency arrays or hash maps for both strings to count occurrences of each character.

3. Compute minimum changes needed

For each character, if the count in the first string exceeds the count in the second, the excess must be changed. Sum these excesses to get the minimum number of changes required.

4. Compare with k

If the minimum changes needed is less than or equal to k, return true; otherwise, return false.

5. Analyze complexity

State that the time complexity is O(n) where n is the length of the strings, and space complexity is O(1) if using a fixed-size array for lowercase letters (or O(c) for character set size).

Key Points to Mention

Anagram definition: two strings with the same character frequencies.
Minimum changes = sum of positive differences between character counts of first and second string.
Alternatively, minimum changes = (sum of absolute differences) / 2.
Edge cases: k >= n (always true), k = 0 (strings must already be anagrams), strings with all same characters.
Time and space complexity: O(n) time, O(1) space for fixed alphabet.
Possible optimization: early exit if k >= n or if minimum changes computed on the fly.

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