Array Questions at Visa: What to Expect

Why Array Matters at Visa

Visa’s coding interview focuses heavily on arrays. With 80 out of 124 total questions dedicated to array problems, this is the single most important data structure to master for their technical screen. This emphasis exists because arrays model real-world data sequences—transaction logs, time-series data, user activity streams—all core to Visa’s financial systems. Solving these problems efficiently demonstrates your ability to handle large-scale, performance-critical data processing, a daily requirement for engineers at Visa.

What to Expect — Types of Problems

You will encounter array problems that test fundamental algorithmic patterns. Expect heavy emphasis on two-pointer techniques for problems involving sorted data or subarray comparisons. Sliding window problems are common for analyzing contiguous subarrays, simulating real-time transaction monitoring. Prefix sum patterns appear for fast range queries, applicable to fraud detection or balance calculations. You will also see problems involving hash maps for frequency counting and in-place array manipulation. The difficulty typically ranges from medium to hard, with a strong focus on optimal time and space complexity. Problems are often framed in a business context, like analyzing purchase patterns or validating transaction sequences.

How to Prepare — Study Tips with One Code Example

Master the core patterns mentioned above. Practice explaining your reasoning aloud as you code. For each problem, identify the pattern first, then implement. Always discuss edge cases (empty arrays, single elements, negative numbers). Time yourself to build speed under pressure.

A key pattern is the two-pointer technique for removing duplicates in-place from a sorted array. This is a fundamental operation for data deduplication.

def remove_duplicates(nums):
    if not nums:
        return 0
    write_index = 1
    for read_index in range(1, len(nums)):
        if nums[read_index] != nums[write_index - 1]:
            nums[write_index] = nums[read_index]
            write_index += 1
    return write_index

Recommended Practice Order

1. Two-Pointer Fundamentals: Start with basic in-place operations (remove element, merge sorted arrays).
2. Sliding Window: Practice fixed and dynamic window problems (maximum subarray, longest substring with K distinct elements).
3. Prefix Sum & Hashing: Solve problems involving subarray sums and frequency maps.
4. Cyclic Sort & In-place Rearrangement: Tackle problems that require rearranging elements within the given array.
5. Hard Pattern Integration: Finally, combine patterns (e.g., sliding window with hash maps) on higher-difficulty problems.

Practice Array at Visa