30+ Amazon SDE-2 Interview Questions and Answers

The task is to find the total number of ways to make change for a specified value using given denominations.

• Use dynamic programming to solve this problem efficiently.

• Create a 2D array to store the number of ways to make change for each value using different denominations.

• Iterate through each denomination and update the array based on the number of ways to make change for each value.

• Return the value at the last cell of the array as the final result.

Determine total number of valid shopping combinations within budget

• Iterate through all possible combinations of items from each array

• Check if the total cost of the combination is within the budget

• Return the count of valid combinations

Find longest continuous patch on a 12 km road with updates in patches

• Maintain a variable to keep track of current patch length

• Update the variable whenever a new patch is added

• Maintain a variable to keep track of longest patch so far

• Compare current patch length with longest patch length and update if necessary

• Use a sorted data structure like a binary search tree to store the patches for efficient search

• Time complexity: O(nlogn) where n is the number of updates by the contracto...read more

Reverse a singly linked list by altering the links between nodes.

• Iterate through the linked list and reverse the links between nodes

• Use three pointers to keep track of the current, previous, and next nodes

• Update the links between nodes to reverse the list

• Return the head of the reversed linked list

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 values less than the node's value.

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

• Ensure that both the left and right subtrees are also binary search trees.

• Traverse the tree in-order and check if the elements are in sorted order.

• Use a recursive function to validate each node's value against its sub...read more

Find the maximum sum submatrix in a given matrix.

• Iterate over all possible submatrices and calculate their sums

• Use Kadane's algorithm to find the maximum sum subarray in each row

• Combine the sums of rows to find the maximum sum submatrix

Find median of integers in a data stream as they are read.

• Use two heaps - max heap for lower half of numbers and min heap for upper half.

• Keep the size of two heaps balanced to find the median efficiently.

• Handle even and odd number of elements separately to calculate median.

• Return vector of medians after each element is read from the stream.

Flatten a multi-level linked list into a single linked list by rearranging the pointers.

• Traverse the linked list and whenever a node has a child, flatten the child list and append it after the current node.

• Update the 'next' and 'child' pointers accordingly while flattening the list.

• Continue this process until all nodes are rearranged into a single linked list.

Given a sentence and a dictionary, construct and return all possible sentences by inserting spaces to form words from the dictionary.

• Use backtracking to generate all possible combinations of words from the dictionary to form sentences.

• Check if a substring of the sentence matches any word in the dictionary, if so, recursively call the function with the remaining substring.

• Continue this process until the entire sentence is segmented into words from the dictionary.

• Return all val...read more

Convert a binary tree into a Greater Tree by updating each node's value to the sum of its original value and the values of all nodes greater than or equal to it.

• Traverse the tree in reverse inorder (right, root, left) to update the nodes' values.

• Keep track of the sum of nodes visited so far to update each node's value.

• Recursively update the node's value by adding the sum of greater nodes to it.

Check if the given string containing only parentheses is balanced or not.

• Use a stack to keep track of opening parentheses.

• Iterate through the string and push opening parentheses onto the stack.

• When a closing parenthesis is encountered, pop from the stack and check if it matches the corresponding opening parenthesis.

• If at the end the stack is empty, return 'YES' else return 'NO'.

The Ninja Port Problem involves finding the minimum time for a ninja to travel between colonies and houses using secret paths and teleportation.

• Calculate the minimum time considering teleportation within colonies, traveling between colonies, and secret paths.

• Keep track of the number of secret paths used and ensure they are one-way.

• Consider the constraints provided to optimize the solution.

• Example: N=2, K=3, S=1, P=1, sourceHouse=1, sourceColony=1, destinationHouse=3, destinat...read more

Clone a binary tree with random pointers and verify if cloning was successful by printing inorder traversal.

• Create a deep copy of the binary tree with random pointers.

• Print the inorder traversal of the cloned binary tree.

• Verify cloning success by printing '1' if successful, '0' otherwise.

Group anagrams together in a list of strings.

• Iterate through the list of strings and sort each string to group anagrams together.

• Use a hashmap to store the sorted string as key and the original string as value.

• Return the values of the hashmap as the grouped anagrams.

Add two numbers represented by linked lists and return the head of the sum list.

• Traverse both linked lists simultaneously while keeping track of carry from previous sum

• Create a new linked list to store the sum of the two numbers

• Handle cases where one linked list is longer than the other by padding with zeros

• Update the sum and carry values accordingly while iterating through the linked lists

Given courses with prerequisites, determine a valid order to complete all courses.

• Create a graph with courses as nodes and prerequisites as edges.

• Use topological sorting to find a valid order to complete all courses.

• Return an empty list if it's impossible to complete all courses.

Implement a priority queue using a heap data structure with push, pop, getMaxElement, and isEmpty functions.

• Implement a priority queue using a max heap data structure.

• Use the provided class structure and complete the push, pop, getMaxElement, and isEmpty functions.

• For push operation, insert the element into the heap and maintain the heap property.

• For pop operation, remove the largest element from the heap.

• For getMaxElement operation, return the largest element from the heap.

• F...read more

Determine the number of good quality bulbs remaining after 'N' rounds of a unique technique.

• Start with all bulbs on in the first round

• Toggle every 'i' bulb in 'i' round

• Count the bulbs that remain on after 'N' rounds

Find the maximum sum by traversing through common elements in two sorted arrays.

• Start with the array containing the smaller first common element

• Switch arrays at common elements to maximize the sum

• Continue adding elements until the end of the arrays

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 left and right subtrees are also binary search trees

Print the boundary nodes of a binary tree in an anti-clockwise direction starting from the root node.

• Traverse the left boundary nodes from top to bottom

• Traverse the leaf nodes from left to right

• Traverse the right boundary nodes from bottom to top

• Handle cases where nodes are null (-1)

• Print the boundary nodes in the specified order

Calculate the total amount of rainwater that can be trapped between given elevations in an elevation map.

• Use two-pointer approach to keep track of left and right boundaries.

• Calculate the trapped water by finding the minimum of left_max and right_max for each bar.

• Subtract the current bar's height from the minimum of left_max and right_max to get the trapped water.

• Keep updating the left_max and right_max as you iterate through the array.

Count the number of islands in a 2D matrix filled with 1s and 0s.

• Iterate through the matrix and perform depth-first search (DFS) to find connected islands.

• Use a visited array to keep track of visited cells to avoid redundant calculations.

• Increment the island count whenever a new island is encountered.

• Consider all eight directions (horizontal, vertical, and diagonal) while exploring the island.

• Handle edge cases like out of bounds and already visited cells.

The task is to find the next greater element for each element in an array to its right, if no greater element exists, return -1.

• Use a stack to keep track of elements for which the next greater element is not found yet.

• Iterate through the array from right to left, popping elements from the stack until a greater element is found.

• Store the next greater element for each element in a separate array.

• If the stack is empty after iterating through the array, it means no greater elemen...read more

Check if given string of parentheses is balanced or not.

• Use a stack to keep track of opening parentheses and pop when a closing parenthesis is encountered.

• If stack is empty at the end and all parentheses are matched, the string is balanced.

• If stack is not empty at the end or mismatched parentheses are encountered, the string is not balanced.

The task is to print the bottom view of a binary tree from left to right.

• Traverse the binary tree in level order and keep track of the horizontal distance of each node from the root.

• For each horizontal distance, update the node value in a map to get the bottom view nodes.

• Print the values of the map in sorted order of horizontal distance to get the bottom view sequence.

Calculate the distance between two nodes in a binary tree.

• Traverse the tree to find the paths from the root to each node

• Find the lowest common ancestor of the two nodes

• Calculate the distance by summing the distances from each node to the common ancestor

Generate all possible combinations of balanced parentheses for a given number of pairs.

• Use recursion to generate all possible combinations of balanced parentheses.

• Keep track of the number of open and close parentheses used in each combination.

• Terminate recursion when the number of open and close parentheses used equals the given number of pairs.

Return a node representing the head of a new Linked List with the sum of the 1st and 2nd half of the given Linked List.

• Split the Linked List into two halves

• Reverse the 2nd half of the Linked List

• Add the corresponding digits from both halves while considering carry

• Create a new Linked List with the sum digits

Given a string, print all possible strings that can be made by placing spaces (zero or one) in between them.

• Use recursion to generate all possible combinations of spaces

• For each recursive call, either add a space or don't add a space between the current character and the next character

• Base case is when there are no more characters left to add spaces between

• Time complexity is O(2^n) where n is the length of the string

Yes, I can design a parking lot using LLD and a tiny URL service using HLD.

• For designing a parking lot using LLD, we can create classes like ParkingLot, ParkingSpot, Vehicle, etc. with their respective attributes and methods.

• For designing a tiny URL service using HLD, we can focus on scalability, fault tolerance, and performance. We can use techniques like sharding, caching, load balancing, etc.

• In the parking lot LLD, we can consider functionalities like assigning spots, chec...read more

Design a data structure with O(1) insert, remove, find-max, and delete-max operations.

• Use a doubly linked list to maintain the elements in sorted order.

• Use a hash table to store the pointers to the nodes in the linked list.

• Maintain a pointer to the maximum element in the hash table.

• Update the pointers in the hash table when inserting or removing elements.

• Update the maximum pointer when deleting or inserting the maximum element.

Find 'k' elements closest to a given number from a stream of characters.

• Use a priority queue to keep track of closest elements.

• Update the queue as new characters come in.

• Return the 'k' closest elements from the queue.

Find sum of all numbers formed from root to leaf path in a binary tree

• Traverse the binary tree using DFS

• At each leaf node, add the number formed from root to leaf path to a sum variable

• Return the sum variable

• Time complexity: O(n)

• Example: For a binary tree with root value 1, left child 2 and right child 3, the sum would be 12 + 13 = 25

Check if a given linked list is a palindrome.

• Traverse the linked list and store the values in an array.

• Compare the first and last elements of the array, then move towards the center.

• If all elements match, the linked list is a palindrome.

• Alternatively, use two pointers to find the middle of the linked list and reverse the second half.

• Compare the first half with the reversed second half to check for a palindrome.

Design a local transport system similar to BMTC

• Introduce a fleet of buses covering various routes within the city

• Implement a smart card system for easy payment and tracking

• Include different types of buses like regular, AC, and Volvo for passenger comfort

• Have designated bus stops with real-time information on bus arrivals

• Offer discounted fares for students and senior citizens

Find median of an unsorted array.

• Sort the array and find the middle element

• Use quickselect algorithm to find the median in O(n) time

• If the array is small, use brute force to find the median

Preorder traversal without recursion

• Use a stack to keep track of nodes

• Push right child first and then left child onto stack

• Pop top of stack and print value

• Repeat until stack is empty