Array Questions at ByteDance: What to Expect

Array questions appear in over half of ByteDance’s technical interviews. With 34 out of 64 total problems tagged as Array, this is the single most tested data structure. Success here is non-negotiable. You need to solve these problems efficiently under pressure, often as the first filter in the interview process.

What to Expect — Types of Problems

ByteDance’s array problems are not about simple iteration. They test your ability to manipulate data under constraints. Expect these core patterns:

1. Sliding Window & Two Pointers: For subarray or substring problems with conditions (e.g., longest substring, minimum window). These questions test optimization.
2. Prefix Sum & Hashing: For problems involving subarray sums or finding relationships between indices and values. A hash map is often the key to an O(n) solution.
3. In-place Array Manipulation: Tasks like rotating an array, moving zeros, or applying transformations without extra space. These test careful index management.
4. Merge Intervals & Sorting: Overlapping schedules, merging ranges, or scheduling problems. Sorting is almost always the first step.
5. Binary Search on Arrays: Even on unsorted-looking arrays, the "search in rotated sorted array" pattern is common. It tests adaptive problem-solving.

The twist is that problems often combine these patterns. A question might start as a sliding window but require a hash map for efficient lookups.

How to Prepare — Study Tips with One Code Example

Master the patterns, not just problems. For each type above, learn the template solution, then practice variations. Focus on writing clean, bug-free code from the first minute. Always state the time and space complexity.

A fundamental pattern is the Two Sum approach using a hash map. It’s the basis for many subarray and pairing problems. Here is the efficient O(n) solution:

def two_sum(nums, target):
    seen = {}
    for i, num in enumerate(nums):
        complement = target - num
        if complement in seen:
            return [seen[complement], i]
        seen[num] = i
    return []

Recommended Practice Order

Do not practice randomly. Build competence in this order:

1. Foundation: Two Sum, Move Zeros, Merge Sorted Array. Get comfortable with basic operations and hash maps.
2. Core Patterns: Practice pure examples of Sliding Window (e.g., Maximum Subarray), Prefix Sum, and In-place manipulation (e.g., Rotate Array).
3. Combination Problems: Tackle problems that merge patterns, like Subarray Sum Equals K (Prefix Sum + Hashing) or Longest Substring Without Repeating Characters (Sliding Window + Hash Map).
4. ByteDance Tagged: Finally, filter to ByteDance’s specific array questions. By this point, you’ll recognize the patterns and can focus on speed and clarity.

Practice Array at ByteDance