Array Questions at Paytm: What to Expect

Array questions form the backbone of Paytm's technical interview process, representing over half of their most frequently asked coding problems. This emphasis stems from the company's core business domains—payments, financial services, and e-commerce—where array manipulation is fundamental. Engineers at Paytm routinely handle transaction logs, user session data, inventory lists, and real-time financial feeds, all of which are modeled and processed as arrays or lists. Mastering array problems demonstrates your ability to work with sequential data, optimize for time and space, and implement efficient algorithms—skills critical for building scalable systems that serve millions of users daily.

What to Expect — Types of Problems

Paytm's array questions typically fall into three key categories, reflecting real-world engineering tasks.

Subarray Problems: These are the most frequent. You'll encounter tasks like finding the maximum sum subarray, subarrays with a given sum, or the longest subarray with specific properties. These test your ability to think in sliding windows or prefix sums, techniques essential for analyzing contiguous data segments, such as detecting fraud patterns in transaction blocks.

Sorting and Searching Variations: Expect modified binary search problems (search in rotated sorted arrays, find first/last occurrence) and questions involving sorting with custom comparators. These simulate scenarios like searching through sorted transaction histories or ranking financial products.

Two-Pointer and In-Place Manipulation: Problems involving merging sorted arrays, removing duplicates in-place, or partitioning arrays (like the Dutch National Flag problem) are common. They assess your skill in efficient memory management, crucial for processing high-volume data streams within constraints.

Less frequently, but importantly, you may see problems involving hashing (finding pairs with a given sum) or basic dynamic programming built on arrays.

How to Prepare — Study Tips with One Code Example

Focus on pattern recognition over memorization. Map each problem type to its core technique: subarray → sliding window/prefix sum, sorted array → binary search, in-place operation → two-pointers. Practice explaining your reasoning aloud, as Paytm interviews evaluate communication alongside code.

A fundamental pattern is the Sliding Window for contiguous subarray problems. Here is a template for finding the length of the longest subarray with a sum less than or equal to a target k.

def longest_subarray_sum_at_most_k(nums, k):
    left = 0
    current_sum = 0
    max_length = 0

    for right in range(len(nums)):
        current_sum += nums[right]

        # Shrink window from left if sum exceeds k
        while current_sum > k and left <= right:
            current_sum -= nums[left]
            left += 1

        # Update max length for valid window
        max_length = max(max_length, right - left + 1)

    return max_length

Recommended Practice Order

1. Foundation: Start with basic traversal, two-sum (hashing), and in-place operations like removing duplicates.
2. Core Patterns: Deep dive into sliding window (fixed & variable size) and prefix sum techniques for subarray problems.
3. Efficiency: Practice binary search variations on sorted arrays and two-pointer techniques for sorting/merging.
4. Integration: Tackle problems combining multiple concepts, like subarray problems that also require hashing.
5. Paytm-Specific: Finally, solve all 15 Paytm-tagged array questions on CodeJeet to familiarize yourself with their exact problem style and difficulty.

Practice Array at Paytm