Meta Follow-up for Custom Sort String (LC791)
Summary
I've shared my insights into Meta's interview style, specifically regarding the 'Custom Sort String' problem (LC791), its common variant, and a crucial optimization follow-up question.
Full Experience
From what I've observed in Meta interviews, they frequently pose the original LeetCode problem 791, 'Custom Sort String'. There's also a minor variant where the order parameter might be presented as a List rather than a string, though this typically doesn't alter the solution significantly. A key aspect of their assessment often comes with a follow-up question: optimizing the character frequency tracking from a HashMap<Character, Integer> to a List<Integer>, which is a good signal if you manage to solve it within time.
Interview Questions (3)
Given two strings order and s. All the characters of order are unique and were sorted in some custom order previously. Permute the characters of s so that they match the order that order was sorted. More specifically, if x occurs before y in order, then x should occur before y in the permuted string. Return any valid permutation of s.
The problem is identical to 'Custom Sort String', but the order parameter is provided as a List<Character> instead of a string. The core logic for sorting characters based on the custom order remains the same, requiring only minor adaptations for handling a list instead of a string.
If the solution for 'Custom Sort String' uses a HashMap<Character, Integer> to store character frequencies, how would you optimize this to use a List<Integer> instead? This typically implies using a fixed-size array (e.g., int[26] for lowercase English letters) to map character ASCII values to array indices for O(1) access.
Preparation Tips
I've detailed my approach and a solution for the original problem, its variant, and the follow-up optimization in my YouTube video. This resource aims to help others prepare effectively for this specific problem pattern often encountered in Meta interviews.