Sharpen your understanding of key data structures and algorithms often assessed in Amazon SDE interviews. This quiz covers important concepts, best practices, and foundational problem-solving techniques to help you excel in technical interview rounds.
If you need to frequently look up whether a word is in a large collection, which data structure is the most efficient for average-case O(1) lookup time?
Explanation: A hash table allows for average-case O(1) lookup time, which makes it ideal for checking membership in large collections. Arrays and queues often require O(n) time for searching because they may need to scan each element. A stack, designed for LIFO operations, is not suitable for random lookups. While arrays and stacks are valuable in specific contexts, hash tables are purpose-built for quick membership checks.
What is the time complexity of binary search on a sorted array with n elements?
Explanation: Binary search works by repeatedly dividing the sorted array in half, resulting in O(log n) time complexity. A linear search (O(n)) is slower as it checks each element. O(n log n) is commonly associated with efficient sorting algorithms, not searching. O(1) would mean constant time regardless of input size, which binary search cannot guarantee.
Which scenario best demonstrates when to use a queue data structure?
Explanation: Queues are first-in, first-out structures, perfect for scenarios like processing tasks as they arrive. Navigating browser history typically uses a stack to allow 'back' navigation. Evaluating arithmetic expressions also utilizes stacks for operator precedence parsing. Recursion call tracking relies on the program’s call stack rather than a queue.
Which option best describes the main characteristic of a singly linked list?
Explanation: A singly linked list is structured so each node holds data and a pointer to the next node, enabling sequential traversal. O(1) access to the middle element suggests random access like in arrays. Doubly linked lists, not singly, have pointers to both previous and next nodes. Unlike arrays, linked list nodes are not necessarily stored in contiguous memory.
Which sorting algorithm is generally most efficient for sorting an array where elements are already nearly sorted?
Explanation: Insertion sort is especially efficient for nearly sorted arrays, performing close to O(n) when only a few elements are out of order. Bubble sort and selection sort, while simple, do not capitalize on the nearly sorted property as effectively. Heap sort is more suitable for large, unsorted datasets, but it does not offer the adaptive performance of insertion sort.
If you need to detect duplicates in a list of integers with the lowest possible time complexity, which data structure should you use?
Explanation: A hash set provides constant-time insertion and lookup, allowing you to quickly check for duplicates as you process each integer. A linked list requires scanning the entire list to check for duplicates, resulting in higher time complexity. Binary heaps are designed for managing ordered elements, not efficient duplicate detection. Queues do not support efficient membership testing.
Given a binary tree, which traversal order visits nodes as: left subtree, root node, right subtree?
Explanation: Inorder traversal visits the left subtree, then the root, then the right subtree, which is particularly useful in binary search trees for obtaining sorted outputs. Preorder visits root before subtrees, postorder does root last, and level order traverses by levels from the root down. Only inorder traversal matches the specified sequence.
Which algorithm relies on a stack to reverse the order of elements in a linear collection?
Explanation: A stack can be used to reverse a string by pushing each character and then popping them off, resulting in reversed order. Breadth First Search uses a queue, not a stack. Finding a Minimum Spanning Tree involves different data structures like sets and priority queues. Merge Sort uses recursion and arrays rather than an explicit stack for this purpose.
Which technique helps find the middle element of a singly linked list in one pass?
Explanation: The tortoise and hare algorithm uses two pointers moving at different speeds to find the midpoint in one traversal. Bubble and sort refers to a sorting method, not linked list traversal. Stacking nodes is not efficient for this task. Binary search requires random access to elements, which linked lists do not support.
What is the time complexity of a function that processes all pairs of elements in an array using two nested loops?
Explanation: Two nested loops over n elements each result in O(n^2) total operations, as each element is paired with every other. O(2n) and O(n) represent linear time, which does not capture the extra work from nesting. O(log n) indicates logarithmic time, typically not associated with nested looping over the same input.