Two Pointers Questions at Infosys: What to Expect

Two Pointers is a core pattern at Infosys, appearing in 26 of their 158 coding questions. That’s roughly 1 in every 6 problems. Mastering this technique is non-negotiable for clearing their technical rounds, as it efficiently solves problems involving arrays, strings, and linked lists—common topics in their online assessments and interviews.

What to Expect — Types of Problems

Infosys primarily uses Two Pointers for three problem types. First, pair search in a sorted array, like finding two numbers that sum to a target. Second, in-place array manipulation, such as removing duplicates or segregating elements (e.g., moving all zeros to the end). Third, sequence comparison, including checking for palindromes or finding the minimum window in a string. These problems test your ability to optimize beyond brute force, often requiring O(n) time and O(1) space. Expect constraints that make naive solutions fail, pushing you toward the two-pointer approach.

How to Prepare — Study Tips with One Code Example

Start by understanding the two main pointer movements: converging pointers (one at the start, one at the end, moving toward the middle) and fast/slow pointers (both starting at the beginning, moving at different speeds). Practice drawing the pointer positions on paper before coding. For Infosys, focus on array-based problems first, as they are most frequent.

A key pattern is the converging pointers solution for the "Two Sum II - Input Array Is Sorted" problem. Here’s how it works across languages:

def two_sum(numbers, target):
    left, right = 0, len(numbers) - 1
    while left < right:
        current_sum = numbers[left] + numbers[right]
        if current_sum == target:
            return [left + 1, right + 1]  # 1-indexed
        elif current_sum < target:
            left += 1
        else:
            right -= 1
    return []

This pattern is fundamental. Practice variations like three-sum or removing duplicates from a sorted array using similar logic.

Recommended Practice Order

Build competence progressively. First, solve basic converging pointer problems (e.g., two sum, palindrome check). Second, tackle in-place array operations (e.g., remove duplicates, move zeros). Third, move to fast/slow pointer problems (e.g., linked list cycle detection). Finally, attempt advanced Infosys-specific problems from their question bank, focusing on constraints like large input sizes. Time yourself to simulate test conditions.

Practice Two Pointers at Infosys