Two Pointers Questions at Samsung: What to Expect

Two Pointers is a critical pattern to master for Samsung coding interviews. With 13 out of their 69 total problems dedicated to this technique, it represents nearly 19% of their question bank—a significant portion that can determine your interview outcome. Samsung frequently uses these problems to assess a candidate’s ability to optimize solutions from O(n²) to O(n) and handle array or string manipulations efficiently. Demonstrating fluency with Two Pointers signals strong analytical skills and preparation.

What to Expect — Types of Problems

Samsung’s Two Pointers questions typically fall into three categories:

1. Sorted Array Pair Searches: Finding pairs that meet a condition (e.g., two-sum variations, triplet sums). These rely on sorting first, then using pointers from both ends.
2. In-Place Array Modifications: Removing duplicates, partitioning arrays, or moving zeros without extra space. One pointer tracks the position to write, another scans the array.
3. Sliding Window Subarray/Substring Problems: Finding contiguous segments satisfying constraints (e.g., longest substring without repeating characters, subarrays with a given sum). Here, two pointers define a window that expands and contracts.

Expect problems that blend these patterns, often involving strings or integer arrays. The focus is on achieving linear time with constant extra space.

How to Prepare — Study Tips with One Code Example

Master the fundamentals: start by understanding when to use opposite-direction pointers versus fast-slow pointers or sliding windows. Practice identifying the sorted condition—many problems require sorting first. Always analyze edge cases: empty inputs, all identical elements, or negative numbers.

A key pattern is the opposite-direction two-pointer search in a sorted array. Below is a classic example: finding a pair that sums to a target.

def two_sum_sorted(nums, target):
    left, right = 0, len(nums) - 1
    while left < right:
        current_sum = nums[left] + nums[right]
        if current_sum == target:
            return [left, right]
        elif current_sum < target:
            left += 1
        else:
            right -= 1
    return [-1, -1]

Recommended Practice Order

Build competence progressively:

1. Start with basic pair searches (Two Sum II, Valid Palindrome).
2. Move to in-place modifications (Remove Duplicates from Sorted Array, Move Zeroes).
3. Tackle sliding window problems (Longest Substring Without Repeating Characters, Minimum Size Subarray Sum).
4. Solve Samsung’s specific problems, focusing on their most frequent patterns.

Prioritize writing clean, bug-free code under time constraints. Simulate interview conditions by verbalizing your thought process as you solve.

Practice Two Pointers at Samsung