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# Algorithms MCQs (Multiple-Choice Questions) and Answers

Algorithms are the set of instructions that are used for solving specific tasks. Here, you will find the set of 50+ multiple-choice questions along with the answers and explanations on algorithms. These **Algorithms MCQs** are written for students as well as professionals to help them prepare for their examinations and interviews. Practice these **Algorithms MCQs** to learn and enhance your skills in **Algorithms**.

## Algorithms MCQs with Answers and Explanations

Here are the top multiple-choice questions and answers on Algorithms:

**1. The primary approach used by the Merge Sort algorithm is ____.**

- Dynamic programming
- Greedy approach
- Divide-and-conquer
- Backtracking

**Answer:** C) Divide-and-conquer

**Explanation:**

Merge Sort follows the divide-and-conquer approach.

**Divide-and-conquer -** This approach divides the array into smaller subarrays, sorts each subarray, and then merges them back together.

**2. What is the best-case time complexity of the Merge Sort algorithm?**

- O(n)
- O(n log n)
- O(n^2)
- O(log n)

**Answer:** B) O(n log n)

**Explanation:**

Merge Sort has a best-case time complexity of O(n log n), the same as its average and worst-case complexities.

**3. Which of the following is a disadvantage of the Merge Sort algorithm?**

- It is not stable.
- It has a worst-case time complexity of O(n^2).
- It is not an in-place sorting algorithm.
- It cannot handle large datasets.

**Answer:** C) It is not an in-place sorting algorithm.

**Explanation:**

Merge Sort requires additional memory to store the merged subarrays. So, it is not an in-place sorting algorithm.

**4. What is the space complexity of Merge Sort?**

- O(1)
- O(log n)
- O(n)
- O(n^2)

**Answer:** C) O(n)

**Explanation:**

Merge Sort requires additional space proportional to the size of the array being sorted, leading to a space complexity of O(n).

**5. Which of the following is a real-world application of Merge Sort?**

- Prim's algorithm
- Sorting large datasets
- Depth-first search
- None of the above

**Answer:** B) Sorting large datasets

**Explanation:**

Merge Sort is particularly useful for sorting large datasets.

**6. What type of graph edges does Dijkstra's Algorithm not handle correctly?**

- Parallel edges
- Negative weights
- Zero-weight edges
- All of the above

**Answer:** C) Zero-weight edges

**Explanation:**

Dijkstra's Algorithm fails with graphs with negative weight edges because it assumes that once a node's shortest path is found, it cannot be improved, which is not true in the presence of negative weights.

**7. The data structure primarily used to implement Dijkstra's Algorithm is ____.**

- Stack
- ArrayList
- Priority Queue
- Linked List

**Answer:** C) Priority Queue

**Explanation:**

A Priority Queue efficiently extracts the minimum distance vertex and updates the shortest paths in Dijkstra's Algorithm.

**8. The best-case time complexity of Dijkstra's Algorithm is ______.**

- O(V^2)
- O(E + V)
- O(V + E log V)
- O(E log V)

**Answer:** D) O(E log V)

**Explanation:**

When using an adjacency list along with a priority queue, the time complexity of Dijkstra's Algorithm is O (E log V), where:

- E is the number of edges
- V is the number of vertices.

**9. One of the best applications of Dijkstra's Algorithm is_____.**

- Google Maps
- Predicting weather patterns
- Sorting a list of numbers
- None of the above

**Answer:** A) Google Maps

**Explanation:**

Dijkstra's algorithm finds shortest paths in Google Maps.

**10. Which of the following problems cannot be solved using Dijkstra's Algorithm?**

- Shortest path in a city map
- Optimal network routing
- Handling graphs with negative weight cycles
- Efficient airline route planning

**Answer:** C) Handling graphs with negative weight cycles

**Explanation:**

Dijkstra's Algorithm does not work correctly with graphs with negative weight cycles.

**11. What is the primary goal of Kruskal's Algorithm?**

- To find the shortest path between two vertices
- To find the minimum spanning tree for a connected weighted graph
- To sort all edges of a graph in descending order
- To traverse a graph using a depth-first search

**Answer:** B) To find the minimum spanning tree for a connected weighted graph

**Explanation:**

Kruskal's Algorithm is designed to find a subset of the edges that form a tree including every vertex, where the total weight of all the edges in the tree is minimised.

**12. In Kruskal's algorithm, first sort all graph edges in increasing order. **

- True
- False
- Can't say anything
- Your choice

**Answer:** A) True

**Explanation:**

In Kruskal's algo, the first step is sorting all the edges of the graph in increasing order.

**13. The time complexity of Kruskalâ€™s algorithm is ____.**

- O (E log E)
- O (V log V)
- O (VE)
- None of the above

**Answer:** A) O (E log E)

**Explanation:**

The time complexity of Kruskalâ€™s algorithm is O (E log E) , where E stands for edges.

**14. Kruskal algorithm is considered a _____.**

- Greedy algorithm
- Brute force approach
- Two-pointer approach
- None of the above

**Answer:** A) Greedy algorithm

**Explanation:**

Kruskal's Algorithm is considered a greedy algorithm because it makes decisions at each step based on the immediate best choice without considering the global optimal solution.

**15. What happens if adding an edge creates a cycle in the spanning tree?**

- The edge is added to the spanning tree
- The algorithm restarts
- The edge is discarded
- The edge's weight is increased

**Answer:** C) The edge is discarded

**Explanation:**

If an edge creates a cycle in the spanning tree, it is discarded to ensure the tree remains acyclic.

**16. Which data structure is primarily used in Breadth-First Search (BFS) to keep track of the vertices to be visited?**

- Stack
- Queue
- Priority Queue
- Linked List

**Answer:** B) Queue

**Explanation:**

BFS uses a queue data structure to maintain the order in which nodes are to be visited.

**17. What is the time complexity of Breadth-First Search (BFS) in a graph with ð‘‰V vertices and EE edges?**

- O(V^2)
- O(E + V)
- O(V + E)
- O(E * V)

**Answer:** C) O(V + E)

**Explanation:**

The time complexity of BFS is O(V + E) because it visits each vertex and each edge once.

**18. In BFS, what condition indicates the presence of a cycle in an undirected graph?**

- If a node is visited twice during traversal.
- If the graph is connected.
- If the graph has more edges than vertices.
- If a node has no adjacent nodes.

**Answer:** A) If a node is visited twice during traversal.

**Explanation:**

In an undirected graph, if BFS encounters a node that has already been visited (and it is not the immediate parent node), it indicates the presence of a cycle.

**19. Fill in the blank: BFS is particularly useful for finding the ____ in an unweighted graph.**

- Shortest path
- Longest path
- Minimal spanning tree
- Maximum flow

**Answer:** A) Shortest path

**Explanation:**

BFS is used to find the shortest path in an unweighted graph because it explores all nodes at the present "depth" level before moving on to nodes at the next depth level.

**20. Which of the following is NOT an application of Breadth-First Search (BFS)?**

- Shortest path finding in an unweighted graph
- Topological sorting in a directed acyclic graph
- Level order traversal of a binary tree
- Finding the minimum spanning tree

**Answer:** D) Finding the minimum spanning tree

**Explanation:**

BFS is not used to find the minimum spanning tree. Algorithms like Kruskal's and Prim's are used for finding the minimum spanning tree.

**21. What is the time complexity of the Karatsuba algorithm for multiplying two binary strings?**

- O(n^2)
- O(n^1.59)
- O(n log n)
- O(n)

**Answer:** B) O(n^1.59)

**Explanation:**

The Karatsuba algorithm uses divide-and-conquer to reduce the number of required multiplications, leading to an O time complexity (n^1.59).

**22. True or False: The Karatsuba algorithm can be applied to any numerical base, not just binary.**

- True
- False
- Can't say
- None

**Answer:** A) True

**Explanation:**

The Karatsuba algorithm is a general multiplication technique that can be applied to numbers in any base, though it's often demonstrated with binary numbers.

**23. The classical method of binary multiplication has a time complexity of ____.**

- O(n log n)
- O(n^2)
- O(n)
- O(n^1.59)

**Answer:** B) O(n^2)

**Explanation:**

The classical method of binary multiplication involves iterating through each bit of the second number and performing shifts and additions, so a time complexity of O(n^2).

**24. Which of the following is NOT a step in the Karatsuba algorithm?**

- Divide the input strings into halves
- Recursively compute the product of the halves
- Multiply the smaller strings directly without recursion
- Combine the results using shifts and additions

**Answer:** C) Multiply the smaller strings directly without recursion

**Explanation:**

The Karatsuba algorithm involves recursive multiplication of the halves. Direct multiplication without recursion is not a part of the Karatsuba method but could be part of the base case handling.

**25. The space complexity of the Karatsuba algorithm is _____.**

- O(n)
- O(1)
- O(n^2)
- None of the above

**Answer:** A) O(n)

**Explanation:**

The space complexity of the Karastuba algorithm is O(n).

**26. What is the primary purpose of the Floyd-Warshall algorithm?**

- To find the shortest path from a single source to all other nodes
- To find the shortest path from a single source to a single destination
- To find the shortest paths between all pairs of nodes
- To find the longest paths between all pairs of nodes

**Answer:** C) To find the shortest paths between all pairs of nodes

**Explanation:**

The Floyd-Warshall algorithm finds the shortest paths between all pairs of nodes in a weighted graph.

**27. The Floyd-Warshall algorithm can handle graphs with which type of edge weights?**

- Only positive edge weights
- Only negative edge weights
- Both positive and negative edge weights
- Only zero edge weights

**Answer:** C) Both positive and negative edge weights

**Explanation:**

The Floyd-Warshall algorithm can handle graphs with positive and negative edge weights but does not work correctly with graphs containing negative cycles.

**28. True or False: The Floyd-Warshall algorithm works for both directed and undirected graphs.**

- True
- False
- Can't say
- None

**Answer:** A) True

**Explanation:**

The Floyd-Warshall algorithm can be applied to both directed and undirected weighted graphs.

**29. The time complexity of the Floyd-Warshall algorithm is ______.**

- O(V^2)
- O(V^2 + E)
- O(V^3)
- O(E^3)

**Answer:** C) O(V^3)

**Explanation:**

The Floyd-Warshall algorithm has a time complexity of O(V^3) due to its three nested loops over the graph vertices.

**30. Which of the following statements is true about the Floyd-Warshall algorithm?**

- It uses a greedy approach.
- It uses dynamic programming.
- It only works with unweighted graphs.
- It can only find the shortest path for a single source.

**Answer:** B) It uses dynamic programming.

**Explanation:**

The Floyd-Warshall algorithm follows a dynamic programming approach to find the shortest paths between all pairs of nodes.

**31. Why is the Floyd-Warshall algorithm better suited for dense graphs rather than sparse graphs?**

- It has a lower time complexity for dense graphs.
- It runs in constant time for dense graphs.
- It ignores the number of edges in the graph.
- It performs the same regardless of graph density.

**Answer:** C) It ignores the number of edges in the graph.

**Explanation:**

The Floyd-Warshall algorithm runs in O(V^3) time regardless of the number of edges.

**32. The Floyd-Warshall algorithm does not work correctly for graphs with ______.**

- Positive cycles
- Zero-weight edges
- Negative cycles
- Directed edges

**Answer:** C) Negative cycles

**Explanation:**

The Floyd-Warshall algorithm does not work correctly for graphs containing negative cycles, as the presence of such cycles can lead to incorrect shortest-path calculations.

**33. Which of the following is the time complexity of the naive recursive implementation of the LCS problem?**

- O(m * n)
- O(m^2)
- O(2^(m+n))
- O(m + n)

**Answer:** C) O(2^(m+n))

**Explanation:**

The naive recursive implementation has an exponential time complexity because it explores all possible subsequences.

**34. The Dynamic Programming approach to LCS has an auxiliary space complexity of O(1).**

- True
- False
- Can't say
- None

**Answer:** B) False

**Explanation:**

The auxiliary space complexity of the standard dynamic programming approach to LCS is O(m * n), where m and n are the lengths of the input strings.

**35. The optimal substructure property of the LCS problem indicates that the problem can be broken down into ____.**

- Smaller unrelated problems
- Subproblems that can be solved independently
- Overlapping subproblems
- Subproblems that build on the solutions of smaller subproblems

**Answer:** D) Subproblems that build on the solutions of smaller subproblems

**Explanation:**

Optimal substructure means the problem can be solved by using the solutions to its subproblems optimally.

**36. In the context of the LCS problem, which approach uses a 2D array to store the lengths of common subsequences?**

- Greedy Algorithm
- Divide and Conquer
- Dynamic Programming (Bottom-Up)
- Backtracking

**Answer:** C) Dynamic Programming (Bottom-Up)

**Explanation:**

The bottom-up dynamic programming approach uses a 2D array to store the lengths of common subsequences.

**37. What is the auxiliary space complexity of the space-optimized bottom-up approach for LCS?**

- O(m * n)
- O(n)
- O(1)
- O(m)

**Answer:** B) O(n)

**Explanation:**

The space-optimized approach uses two arrays of size n, where n is the length of one of the strings.

**38. In the LCS problem, if the last characters of the input strings are the same, the LCS length can be derived as 1 + LCS of ____.**

- Remaining parts of both strings
- One string with the last character removed and the other string unchanged
- Both strings unchanged
- Remaining part of the first string and unchanged second string

**Answer:** A) Remaining parts of both strings

**Explanation:**

If the last characters are the same, we add 1 to the LCS length of the remaining parts of both strings.

**39. The LCS length of the strings 'ABC' and 'CBA' is 2?**

- True
- False
- Can't say
- None

**Answer:** B) False

**Explanation:**

The LCS length of "ABC" and "CBA" is 1. There are common subsequences of length 1.

**40. What type of algorithm is Prim's algorithm?**

- Dynamic Programming
- Divide and Conquer
- Greedy
- Backtracking

**Answer:** C) Greedy

**Explanation:**

Prim's algorithm is a greedy algorithm that builds the MST by selecting the minimum weight edges at each step.

**41. Prim's algorithm starts with an arbitrary vertex and grows the MST by adding the ____ edge that connects a vertex in the MST to a vertex outside the MST.**

- Longest
- Shortest
- Heaviest
- Lightest

**Answer:** D) Lightest

**Explanation:**

At each step, Prim's algorithm selects the minimum weight edge that connects the MST to a vertex outside the MST.

**42. Prim's algorithm can produce different MSTs depending on the starting vertex?**

- True
- False
- Can't say
- None

**Answer:** A) True

**Explanation:**

The choice of the starting vertex can lead to different MSTs, although all will have the same total weight.

**43. In Prim's algorithm, what data structure is commonly used to efficiently select the minimum weight edge?**

- Stack
- Queue
- Priority Queue
- Linked List

**Answer:** C) Priority Queue

**Explanation:**

A priority queue helps in efficiently selecting the edge with the minimum weight at each step.

**44. The complexity of Prim's algorithm when using an adjacency list and a binary heap is ____.**

- O(V^2)
- O(E log V)
- O(E + V)
- O(V log E)

**Answer:** B) O(E log V)

**Explanation:**

When using an adjacency list with a binary heap, Prim's algorithm runs in O(E log V) time.

**45. Prim's algorithm guarantees the same MST irrespective of the starting node?**

- True
- False
- Can't say
- None

**Answer:** B) False

**Explanation:**

While the total weight of the MST will be the same, the structure of the MST can vary depending on the starting vertex.

**46. In Prim's algorithm, what is the initial key value assigned to the starting vertex?**

- Infinity
- -1
- 0
- 1

**Answer:** C) 0

**Explanation:**

The starting vertex is given a key value of 0 to ensure it is picked first.

**47. In the adjacency matrix representation, the time complexity of Prim's algorithm is ____.**

- O(V log E)
- O(V^3)
- O(V^2)
- O(E^2)

**Answer:** C) O(V^2)

**Explanation:**

When using an adjacency matrix, the time complexity of Prim's algorithm is O(V^2) due to the need to check all edges for the minimum weight edge selection.

**48. What is the primary purpose of Kadane's Algorithm?**

- To find the shortest path in a graph
- To find the largest sum of a contiguous subarray
- To sort an array
- To find the minimum sum of a contiguous subarray

**Answer:** B) To find the largest sum of a contiguous subarray

**Explanation:**

Kadane's Algorithm is used to find the subarray with the largest sum within a given array.

**49. The time complexity of Kadane's algorithm is ____.**

- 0(n)
- O(log n)
- O(n^2)
- None of the above

**Answer:** A) 0(n)

**Explanation:**

The time complexity of Kadaneâ€™s algorithm is O(n).

**50. For a given array, what will be the maximum contiguous array sum? int n[]={ -2, -3, 4, -1, -2, 1, 5, -3 };**

- -1
- 10
- 7
- None of the above

**Answer:** C) 7

**Explanation:**

**51. Kadane's Algorithm can be used to find the smallest sum contiguous subarray by negating the elements of the array.**

- True
- False
- Can't say
- None

**Answer:** A) True

**Explanation:**

By negating all elements in the array, Kadane's Algorithm can be used to find the smallest sum contiguous subarray.

**52. Which of the following statements is true about Kadane's Algorithm?**

- It finds the maximum sum of any subarray in O(N^2) time.
- It requires additional space proportional to the size of the array.
- It finds the maximum sum of a contiguous subarray in O(N) time.
- It cannot handle arrays with all negative numbers.

**Answer:** C) It finds the maximum sum of a contiguous subarray in O(N) time.

**Explanation:**

Kadane's Algorithm efficiently finds the maximum sum of a contiguous subarray with a linear time complexity, O(N).

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