Amazon Interview Experience

The assessment evaluated problem-solving, Data Structures and Algorithms knowledge, coding accuracy, and the ability to write efficient solutions within constraints.

Problem 1: Longest Substring Without Repeating Characters

Given a string of length n, find the length of the longest substring without repeating characters.

Constraints: 1 ≤ n ≤ 10⁵ | Time Limit: 1 second

Sample: abcabcbb → 3

Approach: Use two pointers with a sliding window and a set/map. Expand the right pointer, add new characters, update the maximum length, and move the left pointer until duplicates are removed.

Complexity: O(n)

Problem 2: Rotting Oranges

Given a grid containing empty cells (0), fresh oranges (1), and rotten oranges (2), every second a fresh orange adjacent in four directions to a rotten orange becomes rotten. Find the minimum time required, or return -1 if impossible.

Constraints: 1 ≤ N, M ≤ 500 | Time Limit: 1 second

Sample: 3×3 grid with initial rotten orange → minimum time 4

Approach: Put all initially rotten oranges into a queue, count fresh oranges, then perform multi-source BFS level by level. Each level represents one minute. Return -1 if fresh oranges remain.

The interview environment was professional, calm, and well-organized. Instructions were clear, there were no major technical issues, and the interviewer encouraged clear explanations and logical thinking.

Problem 1: Basic Calculator II

Given a string representing an arithmetic expression, evaluate it while respecting operator precedence. Integer division truncates toward zero.

Example: 3+2*2 → 7

Approach: Scan the expression once, build multi-digit numbers, process the previous number whenever an operator appears, immediately handle multiplication/division, accumulate addition/subtraction, and add the final value.

Constraints: T ≤ 10, |STR| ≤ 10⁶, Time Limit: 1 second.

Problem 2: Find The Single Element

Given a sorted array where every number occurs exactly twice except one number, find the number occurring once.

Example: {1, 1, 2, 3, 3, 4, 4} → 2

Approach: XOR every element. Since a ^ a = 0 and a ^ 0 = a, duplicate values cancel and the unique value remains.

Expected complexity: O(n), with an O(log n) solution encouraged.

Candidate Journey

The journey began with strong fundamentals rather than chasing outcomes. Alongside academics, projects and internships built practical understanding of systems, debugging, clarity, and ownership. Setbacks were treated as feedback, leading to continuous refinement of weak areas.

The key lesson was that consistency, strong fundamentals, and belief in the process matter more than shortcuts or last-minute preparation.

Why the Candidate Was Selected

The candidate believes selection came from strong Computer Science fundamentals, a consistent problem-solving approach, and the ability to clearly explain their thinking. Projects and experiences demonstrated ownership, learning ability, and alignment with the role.

Key Takeaways

Build strong fundamentals.

Practice consistently and analyse mistakes.

Explain your thought process clearly.

Gain practical engineering experience through projects and internships.

Treat setbacks as feedback.

Prefer sustained preparation over last-minute study.

Candidate

Anonymous