Understanding Big-O Notation

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Questions and Answers

An algorithm's runtime is observed to remain roughly constant regardless of the input size. Which Big-O notation best describes this algorithm's time complexity?

  • O(1) (correct)
  • O(n²)
  • O(n)
  • O(log n)

Which of the following scenarios would benefit most from an algorithm with O(log n) time complexity?

  • Printing each element in an array.
  • Searching for an element in a sorted array. (correct)
  • Reversing the order of elements in a stack.
  • Finding the largest number in an unsorted list.

Which of the following operations typically exhibits O(1) time complexity?

  • Searching for a specific value in a linked list.
  • Inserting an element at the beginning of a dynamic array.
  • Accessing an element in an array using its index. (correct)
  • Deleting an element from a binary search tree.

Consider an algorithm that iterates through a list to find a specific element. In the worst-case scenario, it checks every element. What is the Big-O time complexity of this algorithm?

<p>O(n) (A)</p>
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Which sorting algorithm generally has a time complexity of O(n log n) in the average case?

<p>Merge Sort (C)</p>
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An algorithm performs the same operation on each pair of elements in a list. What is the Big-O time complexity of this algorithm?

<p>O(n²) (D)</p>
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Which data structure is most likely to use O(log n) time complexity for insertion and deletion operations, assuming it is properly maintained?

<p>Balanced Binary Search Tree (D)</p>
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What is the space complexity typically associated with a recursive algorithm, where h represents the maximum depth of the recursion tree?

<p>O(h) (D)</p>
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Which data structure operation's time complexity is least affected by the size of the data it contains?

<p>Accessing an array element by index (A)</p>
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Assuming a good hash function, what is the average-case time complexity for searching an element in a hash table?

<p>O(1) (B)</p>
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Which of these searching methods has a logarithmic time complexity?

<p>Binary Search (B)</p>
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Consider a scenario where you need to frequently search, insert, and delete elements. Which data structure would be most efficient if the data is unsorted and the size is dynamic?

<p>Balanced Binary Search Tree (C)</p>
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What does Big-O notation primarily describe in the context of algorithms?

<p>How the runtime or space requirements grow as the input size grows (A)</p>
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If an algorithm has a quadratic time complexity, how does the runtime change if the input size doubles?

<p>It quadruples (B)</p>
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Which of the following data structures is most suitable when the priority is fast retrieval by key and order isn't important?

<p>Hash Table (B)</p>
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Which operation demonstrates O(n) time complexity, where n represents the number of elements?

<p>Traversing all nodes in a linked list (A)</p>
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What is a key difference between O(log n) and O(n) complexities in terms of scalability?

<p>O(log n) scales much better with larger datasets compared to O(n). (A)</p>
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In the context of Big-O notation, what does 'n' typically represent?

<p>The size of the input data (B)</p>
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Which of the following best describes the space complexity of an iterative algorithm that uses a few fixed-size variables, irrespective of the input size?

<p>O(1) (D)</p>
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Which search algorithm takes advantage of the ordered nature of data to achieve better performance than a linear search?

<p>Binary Search (C)</p>
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Flashcards

Big-O Notation

Describes how runtime/space needs grow as input grows.

O(1) - Constant Time

Runtime stays constant, regardless of input size.

O(log n) - Logarithmic Time

Runtime grows logarithmically as input size increases.

O(n) - Linear Time

Runtime increases directly with input size.

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O(n log n) - Linearithmic Time

Runtime grows between linear and quadratic.

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O(n²) - Quadratic Time

Runtime increases proportionally to the square of the input size.

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Array Access Time

Accessing an element by its index.

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Linked List Search Time

The algorithm has to search each element to find what it needs.

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Balanced BST Operation Time

Operations maintain balance for optimal lookups.

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Hash Table Operation Time

Fast average-case performance.

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Linear Search Time

Examines each element in sequence until found.

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Binary Search Time

Halves search each step; requires sorted data.

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Study Notes

  • Big-O notation describes how an algorithm's runtime or space needs increase as the input size increases.

Common Big-O Complexities

  • O(1) Constant time reflects the runtime does not change with input size.
  • Examples include accessing an array element by index and stack/queue push/pop operations.
  • O(log n) Logarithmic time reflects the runtime grows logarithmically with input size.
  • Examples include binary search and balanced tree search/insert/delete operations.
  • O(n) Linear time reflects the runtime grows linearly with input size.
  • Examples include linear search and traversing a list/array, and unbalanced tree search.
  • O(n log n) Linearithmic time complexity.
  • Examples include efficient sorting algorithms like merge sort and heap sort.
  • O(n²) Quadratic time complexity.
  • Examples include nested loops and bubble sort/insertion sort algorithms.
  • O(n) operations eventually outgrow O(log n) as n increases, regardless of constants
  • For nested data structures (like graphs), n often represents vertices and m represents edges
  • The height of a complete binary tree with n nodes is approximately log n
  • When analyzing recursive algorithms, the time complexity often depends on the recurrence relation
  • For technical interviews or exams, focus on the dominant term (e.g., O(n² + n) simplifies to O(n²))

Big-O Reminders

  • Array access is O(1).
  • Linked list search/access is O(n).
  • Balanced BST operations are O(log n).
  • AVL/balanced tree operations are O(log n).
  • Hash table operations average case is O(1).
  • Linear search is O(n).
  • Binary search is O(log n).

Space Complexity

  • Recursive algorithms space complexity is often O(h) where h is the recursion tree height.
  • Iterative algorithms space complexity is often O(1) if using fixed extra space, or O(n) if using dynamic data structures.

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