Count longest subsequence in string
Last updated: August 4, 2025
Quick Overview
Given a string, write a function to count the number of longest subsequences that can be formed from the characters of the string. A subsequence is defined as a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements. Your function should take a string as input and return an integer representing the count of the longest subsequences.
Capital One
August 4, 202549
15
3,625 solved
Given a string, write a function to count the number of longest subsequences that can be formed from the characters of the string. A subsequence is defined as a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements. Your function should take a string as input and return an integer representing the count of the longest subsequences.
Capital One uses this problem in the Technical Screen to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
What the Interviewer Expects
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
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 solve this iteratively instead of recursively (or vice versa)?
- How would you test this solution thoroughly?
- What if the input doesn't fit in memory?
- Can you optimize the space complexity of your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of counting the number of longest subsequences in a given string, we can observe that this is a combinatorial problem that can be approached using dynamic programming. The specifi...
Approach
- Calculate the Frequency of Each Character: We will create a frequency map of the characters in the string. For example, for the input 'abcabc', the frequency map will be: `{ 'a': 2, 'b': 2, 'c'...
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