String Questions at Expedia: What to Expect

String manipulation is a core skill tested in Expedia’s technical interviews. With 20 out of 54 total questions tagged as String problems, it’s clear this domain is heavily weighted. For a company that processes vast amounts of travel-related text data—like user queries, destination names, booking codes, and date formats—the ability to efficiently parse, validate, and transform strings is directly relevant to their engineering work. Success here demonstrates you can handle the real-world data processing tasks their systems perform daily.

What to Expect — Types of Problems

Expedia’s String questions tend to focus on practical application over obscure theory. You can generally expect problems in these categories:

• Pattern Matching & Validation: Checking if strings match specific formats (e.g., valid email, phone number, or date string). This often involves regular expressions or careful iteration.
• String Transformation & Parsing: Reformatting data, extracting substrings, or handling encodings. Think tasks like converting a string into a new format or parsing a log entry.
• Anagram & Palindrome Checks: Common fundamentals that test your ability to compare and rearrange string characters using frequency counting or two-pointer techniques.
• String Searching: Finding substrings or patterns within larger text, which may involve implementing or understanding algorithms like KMP for efficiency.
• Interleaving & Merging: Problems where you combine two strings according to specific rules, testing your grasp of dynamic programming or pointer manipulation.

The difficulty often comes from added constraints, such as solving the problem in-place (O(1) extra space) or under tight time complexity requirements.

How to Prepare — Study Tips with One Code Example

Focus on mastering a few key patterns rather than memorizing countless solutions. The Sliding Window technique is essential for problems involving substrings, maximum/minimum length constraints, or character frequency.

1. Map Character Frequency: Use a hash map (or array for fixed alphabets) to count characters.
2. Expand the Window: Move the right pointer to add characters to the window.
3. Shrink from the Left: When the window violates a condition (e.g., contains more than k distinct characters), move the left pointer to shrink it until it’s valid again.
4. Track the Answer: Update your result (e.g., max length) during each valid window state.

Here is a classic example: Longest Substring with At Most K Distinct Characters.

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

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

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

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

    return max_len

Recommended Practice Order

Build your skills progressively. Start with fundamentals, then integrate complexity.

1. Foundation: Palindrome checks, anagram detection, and basic string traversal.
2. Core Patterns: Sliding Window (fixed & variable size), Two Pointers for in-place manipulation.
3. Advanced Techniques: Dynamic Programming for interleaving/edit distance, and KMP for efficient searching.
4. Expedia-Specific: Practice their tagged questions, focusing on the problem types listed above. Simulate interview conditions with time limits.

Practice String at Expedia