Amazon Development Centre India Software Developer Intern Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Easy

There was 2 coding questions
Based on ds and algorithms

Q1. 
Ninja's Pattern with Powers of 2
Ninja, who loves playing with numbers, sets out to arrange numbers within 'N' rows. The unique arrangement follows these rules: the first row contains 1 number, the second...read more
Ans. 
Generate a pattern of numbers in rows following a specific sequence based on powers of 2.
• Start with 1 number in the first row, 2 numbers in the second row, 4 numbers in the third row, and so on based on powers of 2.

• Fill the pattern with numbers in increasing sequence from 1 to 9, recycling back to 1 after reaching 9.

• Output the pattern for a given number 'N' of rows.

• Example: For N = 4, the pattern would be 1, 23, 4567,
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Q2. 
Validate Binary Search Tree (BST)
You are given a binary tree with 'N' integer nodes. Your task is to determine whether this binary tree is a Binary Search Tree (BST).
BST Definition:
A Binary Search Tr...read more
Ans. 
Validate if a given binary tree is a Binary Search Tree (BST) or not.
• Check if the left subtree of a node contains only nodes with data less than the node's data.

• Check if the right subtree of a node contains only nodes with data greater than the node's data.

• Recursively check if both the left and right subtrees are also binary search trees.

• Example: For a node with data 4, left subtree nodes (2, 1, 3) are smaller and righ
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Round duration - 60 minutes
Round difficulty - Easy

There was 2 coding questions based on ds and algorithms

Q1. 
Zig-Zag Array Rearrangement
You are provided with an array of distinct elements, and your task is to rearrange the array elements in a zig-zag manner. Specifically, for every odd index i, the element ARR[...read more
Ans. 
Rearrange array elements in a zig-zag manner where every odd index element is greater than its neighbors.
• Iterate through the array and swap elements to satisfy the zig-zag condition.

• Ensure that for every odd index i, ARR[i] > ARR[i-1] and ARR[i] > ARR[i+1].

• Multiple correct answers may exist for a given array.
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Q2. 
Flatten a Linked List
You are provided with a linked list of 'N' nodes. Each node contains two pointers: NEXT, pointing to the next node in the list, and CHILD, pointing to a linked list. Each child linke...read more
Ans. 
Flatten a linked list of sorted child linked lists into a single sorted linked list.
• Traverse the linked list and maintain a priority queue to keep track of the next smallest element.

• Merge the child linked lists into the priority queue while traversing the main linked list.

• Pop elements from the priority queue to create the final flattened linked list.
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Round duration - 45 Minutes
Round difficulty - Medium

My interview started at 9:30 and it took around 45 minutes to complete my interview.This was held on Amazon Chime and the interview lasted for 1 hour. Firstly the interviewer asked to introduce about myself, later asked regarding the projects I have mentioned in my resume. Then started displaying the coding question. The first question is number of islands in a matrix.

Q1. 
Number of Islands Problem Statement
You are provided with a 2-dimensional matrix having N rows and M columns, containing only 1s (land) and 0s (water). Your goal is to determine the number of islands in t...read more
Ans. 
Count the number of islands in a 2D matrix of 1s and 0s.
• Use Depth First Search (DFS) or Breadth First Search (BFS) to traverse the matrix and identify connected groups of 1s.

• Maintain a visited array to keep track of visited cells to avoid redundant traversal.

• Increment the island count each time a new island is encountered.

• Consider edge cases like when the matrix is empty or all cells are water (0s).
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Round duration - 90 minutes
Round difficulty - Easy

This was an online technical round on the mettl platform, the test window was open from 22 to 25 May 2020
The test had 28 mcqs and 2 coding questions.
The test was proctored. One needed to have webcam on.
A sample test link was provided before test to get familiar with the mettl platform.

Q1. 
Count Inversions Problem Statement
Given an integer array ARR of size N, your task is to find the total number of inversions that exist in the array.
An inversion is defined for a pair of integers in the...read more
Ans. 
Count the total number of inversions in an integer array.
• Iterate through the array and for each pair of elements, check if the conditions for inversion are met.

• Use a nested loop to compare each pair of elements efficiently.

• Keep a count of the inversions found and return the total count at the end.
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Q2. 
Find Pair with Maximum GCD in an Array
Given an array of positive integers, your task is to find the GCD (Greatest Common Divisor) of a pair of elements such that it is the maximum among all possible pair...read more
Ans. 
Find the pair with the maximum GCD in an array of positive integers.
• Iterate through all pairs of elements in the array.

• Calculate the GCD of each pair using Euclidean algorithm.

• Keep track of the maximum GCD found so far.

• Return the maximum GCD value.
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Round duration - 60 minutes
Round difficulty - Medium

Time : 12pm to 1pm
Mode of Interview : Amazon Chime Video
LiveCode : To write code, it was not a compiler
The interviewer was quite supportive.

Q1. 
Majority Element Problem Statement
Given an array/list 'ARR' consisting of 'N' integers, your task is to find the majority element in the array. If there is no majority element present, return -1.
Exampl...read more
Ans. 
Find the majority element in an array, return -1 if no majority element exists.
• Iterate through the array and keep track of the count of each element using a hashmap.

• Check if any element's count is greater than floor(N/2) to determine the majority element.

• Return the majority element or -1 if no majority element exists.
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Q2. 
Subarray with Equal Occurrences Problem Statement
You are provided with an array/list ARR of length N containing only 0s and 1s. Your goal is to determine the number of non-empty subarrays where the numbe...read more
Ans. 
Count the number of subarrays where the number of 0s is equal to the number of 1s in a given array of 0s and 1s.
• Iterate through the array and keep track of the count of 0s and 1s encountered so far.

• Use a hashmap to store the difference between the counts of 0s and 1s seen at each index.

• Increment the count of subarrays whenever the difference between the counts seen before matches the current difference.
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Round duration - 60 minutes
Round difficulty - Medium

Time : 11 am to 12am
Mode of Interview : Amazon Chime Video
LiveCode : To write code, it was not a compiler
The interviewer was quite supportive.

Q1. 
Sorted Linked List to Balanced BST Problem Statement
Given a singly linked list where nodes contain values in increasing order, your task is to convert it into a Balanced Binary Search Tree (BST) using th...read more
Ans. 
Convert a sorted linked list into a Balanced Binary Search Tree (BST) using the same data values.
• Create a function to convert the linked list to an array for easier manipulation.

• Implement a function to build a Balanced BST from the array recursively.

• Ensure the height difference of the subtrees is no more than 1 for each node.

• Use level order traversal to output the values of the BST nodes.

• Handle NULL nodes by representi
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Q2. 
Implement Stack with Linked List
Your task is to implement a Stack data structure using a Singly Linked List.
Explanation:
Create a class named Stack which supports the following operations, each in O(1...read more
Ans. 
Implement a Stack data structure using a Singly Linked List with operations in O(1) time.
• Create a class named Stack with getSize, isEmpty, push, pop, and getTop methods.

• Use a Singly Linked List to store the elements of the stack.

• Ensure each operation runs in O(1) time complexity.

• Handle edge cases like empty stack appropriately.

• Test the implementation with sample queries to verify correctness.
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