Transform string to hash map
Last updated: November 13, 2025
Quick Overview
Given a string, transform it into a hash map where each unique character in the string is a key, and its corresponding value is the number of times that character appears in the string. The output should be a hash map (or dictionary) representing this character frequency count.
Twilio
November 13, 2025302
14
875 solved
Given a string, transform it into a hash map where each unique character in the string is a key, and its corresponding value is the number of times that character appears in the string. The output should be a hash map (or dictionary) representing this character frequency count.
This coding problem is frequently asked during Technical Screen at Twilio. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Twilio expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- Can you optimize the space complexity of your solution?
- What happens if the input contains duplicates?
- What if the input doesn't fit in memory?
- Can you solve this in a single pass?
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Problem Analysis
The task requires us to create a hash map (or dictionary) that counts the occurrences of each unique character in a given string. This problem can be effectively solved using a hash map (dictionary in...
Approach
- Initialize an empty dictionary to store character counts.
- Iterate through each character in the string:
- If the character is not already a key in the dictionary, add it with a value of 1. ...
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