Array Questions at Turing: What to Expect

Array questions make up 25 of the 40 total problems in Turing's technical interview process. This 62.5% concentration means your performance on array manipulation directly determines your interview outcome. Arrays are the fundamental data structure for storing sequential data, and questions about them test core algorithmic skills like iteration, pointer manipulation, and efficient searching—skills that are immediately applicable to real-world backend and data processing tasks Turing's clients need. Mastering these problems is not optional; it's the primary technical gate you must pass.

What to Expect — Types of Problems

Turing's array questions focus on practical, pattern-based problems rather than obscure computer science theory. You can expect three main categories:

1. In-Place Operations: Modifying the array without using significant extra space. This includes tasks like removing duplicates, moving zeros, or applying rotations directly within the given array structure.
2. Two-Pointer Techniques: Using indices to track positions, often to solve problems involving searching for pairs, reversing elements, or handling sorted sequences. This pattern is crucial for achieving O(n) time complexity.
3. Prefix Sum or Sliding Window: Calculating running totals to answer range queries quickly or using a dynamic window to find subarrays that meet a specific condition (e.g., maximum sum, shortest length with a given sum).

The difficulty progresses from basic traversal to combining multiple patterns in a single problem.

How to Prepare — Study Tips with One Code Example

Focus on pattern recognition, not memorization. Understand the underlying technique for each problem category. Practice by first solving the problem, then analyzing time/space complexity, and finally, writing clean, production-ready code without comments.

A key pattern to internalize is the Two-Pointer technique for in-place element removal. Here is a standard solution for removing all instances of a given value val from an array, in-place, returning the new length.

def removeElement(nums, val):
    k = 0  # Pointer for the position of the next non-val element
    for i in range(len(nums)):
        if nums[i] != val:
            nums[k] = nums[i]
            k += 1
    return k  # First k elements now contain the valid result

The pattern uses index k to build the new array from the front, overwriting positions only with valid elements. This runs in O(n) time and uses O(1) extra space.

Recommended Practice Order

1. Start with fundamental traversal and in-place modification (e.g., Remove Duplicates, Remove Element).
2. Master the Two-Pointer technique in its various forms (converging pointers, fast-slow pointers).
3. Tackle Sliding Window problems to understand dynamic subarray analysis.
4. Combine patterns for more complex challenges, like using hash maps with arrays for two-sum problems or prefix sums for range calculations.
5. Finally, simulate interview conditions by solving Turing's array problems under a time limit.

Practice Array at Turing