String Questions at Zeta: What to Expect

String manipulation is a core skill tested in Zeta’s technical interviews. With 10 out of their 35 total coding questions focused on strings, it’s clear they prioritize this domain. Why? Financial technology platforms like Zeta handle vast amounts of textual data—transaction descriptions, log parsing, user input validation, and protocol communication. Efficiently processing, transforming, and validating this data is critical for performance and reliability. A candidate’s ability to write clean, optimal string code directly reflects their capacity to work with real-world fintech data pipelines and APIs.

What to Expect — Types of Problems

Zeta’s string questions typically fall into a few key categories. Pattern Matching and Parsing is common, where you might need to validate or extract data from formatted strings (like log entries or transaction strings). Anagram and Palindrome variations test your grasp of character frequency and two-pointer techniques. String Transformation problems ask you to modify a string according to specific rules, often involving in-place operations or careful iteration. Finally, Sliding Window on Strings appears frequently for finding substrings meeting certain criteria, such as the longest substring without repeating characters or a substring containing all characters of another string. Expect constraints that require O(n) time complexity, making brute-force solutions unacceptable.

How to Prepare — Study Tips with One Code Example

Focus on mastering a few core techniques: the two-pointer approach (for palindromes or reversing), hash maps for character counting (anagrams, first unique char), and the sliding window algorithm for substring problems. Practice writing these patterns from memory. Always clarify edge cases: empty strings, case sensitivity, and Unicode characters. For each problem, first articulate a brute-force solution, then optimize.

A fundamental pattern is the Sliding Window for finding the longest substring with at most K distinct characters. This is a classic Zeta-style problem that tests your ability to manage a dynamic window and a frequency map.

def longest_substring_k_distinct(s, k):
    char_count = {}
    left = 0
    max_len = 0

    for right in range(len(s)):
        char_count[s[right]] = char_count.get(s[right], 0) + 1

        while len(char_count) > k:
            char_count[s[left]] -= 1
            if char_count[s[left]] == 0:
                del char_count[s[left]]
            left += 1

        max_len = max(max_len, right - left + 1)

    return max_len

Recommended Practice Order

Build competency progressively. Start with basic reversal and palindrome checks. Move to anagram detection using hash maps. Then, tackle core sliding window problems (like the example above). After that, practice more complex parsing and transformation problems, which often combine these patterns. Finally, attempt Zeta’s specific tagged questions to familiarize yourself with their problem style and constraints. Time yourself to simulate interview pressure.

Practice String at Zeta