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All questions of Hashmaps for Software Development Exam

Which of the following best describes a hashmap?
a)
An ordered collection of key-value pairs.
b)
A data structure that allows duplicate values.
c)
A data structure that provides constant-time access to elements based on their keys.
d)
A collection of elements sorted in ascending order.
Correct answer is option 'C'. Can you explain this answer?

Aashna Sharma answered

Hashmap

Hashmap is a data structure that provides constant-time access to elements based on their keys. This means that regardless of the size of the hashmap, the time taken to retrieve an element is the same, making it very efficient for lookups.

Key Characteristics of Hashmap:

- Key-Value Pairs: A hashmap is a collection of key-value pairs where each key is unique.
- Constant-Time Access: Hashmap allows for constant-time access to elements based on their keys, making it very efficient for retrieving values.
- Hashing Function: Hashmap uses a hashing function to map keys to their corresponding values, allowing for quick lookup.
- Dynamic Sizing: Hashmap can dynamically resize itself to accommodate more elements without affecting performance.
- No Duplicate Keys: Hashmap does not allow duplicate keys, ensuring each key is unique in the collection.

Benefits of Using Hashmap:

- Efficient Lookups: Hashmap provides constant-time access to elements, making it ideal for applications requiring fast retrieval of data.
- Flexibility: Hashmap can store a wide range of data types as values, providing flexibility in how data is stored and accessed.
- Scalability: Hashmap can grow in size as more elements are added, ensuring optimal performance even with large datasets.
- Easy to Use: Hashmap is easy to use and implement, making it a popular choice for developers in various programming languages.

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Which of the following hashing techniques uses the concept of linear probing?
a)
Separate chaining
b)
Quadratic probing
c)
Double hashing
d)
Cuckoo hashing
Correct answer is option 'A'. Can you explain this answer?

Tech Era answered

Linear probing is a technique used in open addressing, not separate chaining. Separate chaining uses linked lists to handle collisions.

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Which of the following is a drawback of using separate chaining for collision resolution?
a)
Increased memory usage due to linked lists.
b)
Inefficient search operation for large hashmaps.
c)
Difficulty in implementing the hashmap data structure.
d)
High probability of collisions.
Correct answer is option 'A'. Can you explain this answer?

Tech Era answered

Separate chaining requires additional memory to store linked lists for collisions, leading to increased memory usage compared to open addressing.

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Which of the following statements about open addressing is false?
a)
Open addressing avoids the use of auxiliary data structures for collision resolution.
b)
Open addressing requires all keys to be stored in the hashmap itself.
c)
Open addressing can lead to clustering when many collisions occur.
d)
Open addressing can handle more elements than separate chaining.
Correct answer is option 'D'. Can you explain this answer?

Aryan Ghosh answered

Open addressing is a technique used for resolving collisions in a hash table. In open addressing, when a collision occurs (i.e., when two keys hash to the same index), the algorithm looks for the next available slot in the table to store the key-value pair.

Statement D states that open addressing can handle more elements than separate chaining. However, this statement is false, as open addressing has a limitation on the number of elements it can handle, whereas separate chaining does not have such a limitation.

Open addressing vs Separate chaining
To understand why statement D is false, it is important to compare open addressing with separate chaining.

- Open addressing:
- In open addressing, all keys are stored in the hashmap itself. This means that the size of the hashmap needs to be determined in advance, and it cannot be dynamically resized.
- When a collision occurs, open addressing uses a probing sequence to find the next available slot in the table. This probing sequence can be linear, quadratic, or double hashing.
- If the table becomes full and there are no more available slots for storing new elements, it becomes impossible to insert additional elements. This is known as hash table overflow.
- Open addressing can lead to clustering when many collisions occur. Clustering refers to the phenomenon where consecutive slots in the table become occupied, leading to longer probe sequences.

- Separate chaining:
- In separate chaining, each slot in the hashmap is a linked list that stores all the key-value pairs hashing to that index.
- Separate chaining does not require all keys to be stored in the hashmap itself. The hashmap can dynamically resize and accommodate more elements as needed.
- When a collision occurs, the key-value pair is added to the linked list at the corresponding index.
- Separate chaining does not suffer from clustering, as the linked lists can grow independently without affecting the performance of other slots.

Conclusion:
Statement D is false because open addressing cannot handle more elements than separate chaining. Open addressing has a limitation on the number of elements it can handle, as it requires the size of the hashmap to be determined in advance. In contrast, separate chaining can dynamically resize and accommodate more elements as needed, making it more flexible in handling a larger number of elements.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<int, std::string> colors;
colors[1] = "Red";
colors[2] = "Green";
colors[3] = "Blue";
std::cout << colors[2];
return 0;
}
a)
Red
b)
Green
c)
Blue
d)
Compilation Error
Correct answer is option 'B'. Can you explain this answer?

Tom Tattle answered

The code defines an unordered_map with integer keys and string values. The value associated with key 2 is "Green". So, the output will be "Green".

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The Rabin-Karp algorithm uses which of the following concepts?
a)
Rolling hash function
b)
Quadratic probing
c)
Separate chaining
d)
Heap data structure
Correct answer is option 'A'. Can you explain this answer?

Tech Era answered

The Rabin-Karp algorithm uses a rolling hash function to efficiently compare the pattern string with substrings of the text string.

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In a hashmap, how is the size of the underlying array typically chosen?
a)
It is fixed during initialization
b)
It is determined based on the number of elements stored
c)
It is equal to the maximum number of elements that can be stored
d)
It is set to a random value
Correct answer is option 'B'. Can you explain this answer?

Code Nation answered

The size of the underlying array for a hashmap is typically chosen based on the number of elements stored to achieve a good load factor and reduce collisions.

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Which of the following statements is true about hashmaps in C++?
a)
Hashmaps store elements in a sorted manner.
b)
Hashmaps guarantee constant-time complexity for all operations.
c)
Hashmaps can only store integer values.
d)
Hashmaps do not allow duplicate keys.
Correct answer is option 'D'. Can you explain this answer?

KnowIT answered

Hashmaps in C++ do not allow duplicate keys. Each key in a hashmap must be unique.

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What is the purpose of a hash function in a hashmap?
a)
To determine the size of the hashmap
b)
To compute the index where an element will be stored
c)
To sort the elements in the hashmap
d)
To remove duplicate elements from the hashmap
Correct answer is option 'B'. Can you explain this answer?

KnowIT answered

A hash function in a hashmap is used to compute the index or hash value of an element, which determines where it will be stored in the hashmap.

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Which of the following collision resolution techniques is used in separate chaining?
a)
Linear probing
b)
Quadratic probing
c)
Double hashing
d)
Linked lists
Correct answer is option 'D'. Can you explain this answer?

Yogesh Dwivedi answered

Separate chaining uses linked lists to handle collisions. Each slot of the hashmap contains a linked list of key-value pairs.

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The Rabin-Karp algorithm is primarily used for which of the following?
a)
Hashing passwords
b)
String matching
c)
Searching in a binary tree
d)
Sorting arrays
Correct answer is option 'B'. Can you explain this answer?

Yogesh Dwivedi answered

The Rabin-Karp algorithm is primarily used for string matching. It efficiently finds occurrences of a pattern string within a longer text string.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<char, int> map;
map['a'] = 1;
map['b'] = 2;
map['c'] = 3;
map['d'] = 4;
std::cout << map['z'] << std::endl;
return 0;
}
a)
0
b)
Compilation error
c)
Runtime error
d)
Garbage value
Correct answer is option 'A'. Can you explain this answer?

Anil Kumar answered

The code assigns values to keys 'a' to 'd', but the key 'z' is not assigned a value. Accessing map['z'] will return a default-constructed value, which is 0 for integers.

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In C++, which header file is required to use the unordered_map class?
a)
<vector>
b)
<array>
c)
<map>
d)
<unordered_map>
Correct answer is option 'D'. Can you explain this answer?

Tanuja Mishra answered

To use the unordered_map class in C++, the header file <unordered_map> needs to be included.

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What is the purpose of open addressing in hashmaps?
a)
To handle collisions by storing multiple values for the same key.
b)
To convert a key into an array index.
c)
To resize the hashmap dynamically.
d)
To find the next available slot when a collision occurs.
Correct answer is option 'D'. Can you explain this answer?

Yogesh Dwivedi answered

Open addressing is used to find the next available slot in the hashmap when a collision occurs. It avoids storing multiple values for the same key.

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What is hashing in the context of hashmaps?
a)
A technique for sorting elements in a hashmap.
b)
A method for converting a key into an array index.
c)
The process of resizing a hashmap to accommodate more elements.
d)
The operation of removing an element from a hashmap.
Correct answer is option 'B'. Can you explain this answer?

Yogesh Dwivedi answered

Hashing is a method for converting a key into an array index using a hash function. The hash function maps the key to an array index.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<int, int> map;
map[1] = 10;
map[2] = 20;
map[3] = 30;
map[4] = 40;
map.erase(2);
std::cout << map.size() << std::endl;
return 0;
}
a)
1
b)
2
c)
3
d)
4
Correct answer is option 'C'. Can you explain this answer?

Tech Era answered

The code assigns values to four different keys in the hashmap and then erases the key 2. The 'size()' function returns the number of elements in the hashmap, which is 3 after erasing.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<int, int> map;
for (int i = 0; i < 5; i++) {
map[i] = i * 10;
}
std::cout << map[5] << std::endl;
return 0;
}
a)
0
b)
10
c)
40
d)
Garbage value
Correct answer is option 'D'. Can you explain this answer?

Tech Era answered

The code assigns values to keys from 0 to 4, but the key 5 is not assigned a value. Accessing map[5] will return a default-constructed value, which is 0 for integers.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<int, int> numbers;
numbers[1] = 10;
numbers[2] = 20;
numbers[3] = 30;
numbers[4] = 40;
std::cout << numbers[5];
return 0;
}
a)
0
b)
10
c)
20
d)
Compilation Error
Correct answer is option 'A'. Can you explain this answer?

Tom Tattle answered

The code defines an unordered_map with integer keys and integer values. The key 5 is not present in the map, so accessing it will return the default value for integers, which is 0.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<int, std::string> map;
map[1] = "Alice";
map[2] = "Bob";
map[3] = "Charlie";
std::cout << map[2] << std::endl;
return 0;
}
a)
Alice
b)
Bob
c)
Charlie
d)
Compilation error
Correct answer is option 'B'. Can you explain this answer?

Tech Era answered

The code assigns values to keys in the hashmap and then retrieves the value associated with the key 2, which is "Bob". The output will be "Bob".

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<int, int> map;
map[1] = 10;
map[2] = 20;
map[3] = 30;
map[4] = 40;
std::cout << map.size() << std::endl;
return 0;
}
a)
1
b)
2
c)
3
d)
4
Correct answer is option 'D'. Can you explain this answer?

Anil Kumar answered

The code assigns values to four different keys in the hashmap. The 'size()' function returns the number of elements in the hashmap, which is 4 in this case.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<int, std::string> colors;
colors[1] = "Red";
colors[2] = "Green";
colors[3] = "Blue";
std::unordered_map<int, std::string>::iterator it;
for (it = colors.begin(); it != colors.end(); it++) {
std::cout << it->second << " ";
}
return 0;
}
a)
Red Green Blue
b)
Blue Green Red
c)
Green Red Blue
d)
Compilation Error
Correct answer is option 'D'. Can you explain this answer?

Coders Trust answered

The code snippet is incomplete and does not have an output.

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What is the time complexity of searching for an element in a hashmap?
a)
O(1)
b)
O(log n)
c)
O(n)
d)
O(n^2)
Correct answer is option 'A'. Can you explain this answer?

KnowIT answered

Searching for an element in a hashmap has an average time complexity of O(1). However, in the worst case scenario, it can be O(n) if all elements collide.

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Which data structure is commonly used to implement hashmaps?
a)
Linked list
b)
Array
c)
Stack
d)
Binary tree
Correct answer is option 'A'. Can you explain this answer?

KnowIT answered

Hashmaps are commonly implemented using an array of linked lists. This allows handling collisions by chaining.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<std::string, int> ages;
ages["John"] = 25;
ages["Alice"] = 30;
ages["Bob"] = 35;
std::cout << ages["Alice"];
return 0;
}
a)
25
b)
30
c)
35
d)
Compilation Error
Correct answer is option 'B'. Can you explain this answer?

Tom Tattle answered

The code defines an unordered_map with string keys and integer values. The value associated with the key "Alice" is 30. So, the output will be 30.

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What will be the output of the following code?
#include <iostream>
#include <unordered_map>
int main() {
std::unordered_map<char, int> frequencies;
frequencies['a'] = 2;
frequencies['b'] = 3;
frequencies['c'] = 1;
std::cout << frequencies['d'];
return 0;
}
a)
0
b)
1
c)
2
d)
Compilation Error
Correct answer is option 'A'. Can you explain this answer?

Coders Trust answered

The code defines an unordered_map with character keys and integer values. The key 'd' is not present in the map, so accessing it will return the default value for integers, which is 0.

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What is the time complexity of finding the maximum element in a hashmap?
a)
O(1)
b)
O(log n)
c)
O(n)
d)
O(n^2)
Correct answer is option 'C'. Can you explain this answer?

Tanuj Arora answered

Finding the maximum element in a hashmap requires traversing all the elements, resulting in a time complexity of O(n).

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Which of the following collision resolution techniques is used in open addressing?
a)
Linked lists
b)
Red-black trees
c)
Linear probing
d)
Hash functions
Correct answer is option 'C'. Can you explain this answer?

Anil Kumar answered

Linear probing is a collision resolution technique used in open addressing. It probes the next slot in a linear fashion until an available slot is found.

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In case of a collision in a hashmap, which technique is commonly used to handle it?
a)
Chaining
b)
Sorting
c)
Rehashing
d)
Partitioning
Correct answer is option 'A'. Can you explain this answer?

KnowIT answered

Chaining is a common technique used to handle collisions in hashmaps. It involves storing multiple elements with the same hash value in the same location using linked lists.

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Which of the following is an advantage of using a hashmap over an array?
a)
Hashmaps have a fixed size
b)
Hashmaps can store elements in a sorted manner
c)
Hashmaps provide constant-time complexity for all operations
d)
Hashmaps have a lower space complexity
Correct answer is option 'C'. Can you explain this answer?

Code Nation answered

Hashmaps provide constant-time complexity for insertion, deletion, and searching operations, making them efficient for handling large datasets.

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Which of the following operations can be performed in O(1) time for a hashmap?
a)
Insertion
b)
Deletion
c)
Searching
d)
All of the above
Correct answer is option 'D'. Can you explain this answer?

Tanuj Arora answered

Insertion, deletion, and searching operations can be performed in O(1) time complexity for a hashmap.

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All questions of Hashmaps for Software Development Exam

Which of the following hashing techniques uses the concept of linear probing?
a)
Separate chaining
b)
Quadratic probing
c)
Double hashing
d)
Cuckoo hashing
Correct answer is option 'A'. Can you explain this answer?

The Rabin-Karp algorithm uses which of the following concepts?
a)
Rolling hash function
b)
Quadratic probing
c)
Separate chaining
d)
Heap data structure
Correct answer is option 'A'. Can you explain this answer?

What is the purpose of a hash function in a hashmap?
a)
To determine the size of the hashmap
b)
To compute the index where an element will be stored
c)
To sort the elements in the hashmap
d)
To remove duplicate elements from the hashmap
Correct answer is option 'B'. Can you explain this answer?

Which of the following collision resolution techniques is used in separate chaining?
a)
Linear probing
b)
Quadratic probing
c)
Double hashing
d)
Linked lists
Correct answer is option 'D'. Can you explain this answer?

The Rabin-Karp algorithm is primarily used for which of the following?
a)
Hashing passwords
b)
String matching
c)
Searching in a binary tree
d)
Sorting arrays
Correct answer is option 'B'. Can you explain this answer?

In C++, which header file is required to use the unordered_map class?
a)
<vector>
b)
<array>
c)
<map>
d)
<unordered_map>
Correct answer is option 'D'. Can you explain this answer?

What is the time complexity of searching for an element in a hashmap?
a)
O(1)
b)
O(log n)
c)
O(n)
d)
O(n^2)
Correct answer is option 'A'. Can you explain this answer?

Which data structure is commonly used to implement hashmaps?
a)
Linked list
b)
Array
c)
Stack
d)
Binary tree
Correct answer is option 'A'. Can you explain this answer?

What is the time complexity of finding the maximum element in a hashmap?
a)
O(1)
b)
O(log n)
c)
O(n)
d)
O(n^2)
Correct answer is option 'C'. Can you explain this answer?

Which of the following collision resolution techniques is used in open addressing?
a)
Linked lists
b)
Red-black trees
c)
Linear probing
d)
Hash functions
Correct answer is option 'C'. Can you explain this answer?

In case of a collision in a hashmap, which technique is commonly used to handle it?
a)
Chaining
b)
Sorting
c)
Rehashing
d)
Partitioning
Correct answer is option 'A'. Can you explain this answer?

Which of the following operations can be performed in O(1) time for a hashmap?
a)
Insertion
b)
Deletion
c)
Searching
d)
All of the above
Correct answer is option 'D'. Can you explain this answer?

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