Data Structures: Priority Queue and Double-ended Queue

Questions and Answers

What is the primary distinguishing feature of a priority queue?

Each element has an associated priority (correct)

Elements are served in the order they are inserted

Elements can only be inserted at the end

Elements can only be removed from the front

What is a common use case for a double-ended queue (deque)?

Graph traversal

Binary search trees

Job scheduling

Sliding window algorithms (correct)

What is a key characteristic of a tree data structure?

It has a hierarchical organization (correct)

Elements can only be inserted at the end

It can only have a maximum of two child nodes

It is a linear data structure

What is the main difference between stack and heap memory allocation in C++?

Stack allocation happens on contiguous blocks of memory Signup and view all the answers

What is the purpose of a priority queue in job scheduling?

To schedule jobs based on their priority Signup and view all the answers

Which of the following is a common operation in a tree data structure?

Traversing the tree in pre-order Signup and view all the answers

What is the primary advantage of using heap memory allocation?

Ability to handle larger allocations Signup and view all the answers

What is the advantage of using a deque over a regular queue?

Elements can be inserted or removed from both ends Signup and view all the answers

What is a characteristic of objects and variables allocated on the heap?

They have a lifetime beyond the scope of a function call Signup and view all the answers

What is the significance of heap memory allocation in C++?

It is used for dynamic memory allocation Signup and view all the answers

What is a disadvantage of heap memory allocation?

Increased memory fragmentation Signup and view all the answers

Why is heap memory allocation slower than stack allocation?

Because it involves more complex management Signup and view all the answers

What happens to memory allocated on the heap when it is no longer needed?

It remains allocated until explicitly de-allocated using delete Signup and view all the answers

What is an example of a situation where heap memory allocation is particularly useful?

When handling user input Signup and view all the answers

What is a consequence of memory fragmentation on the heap?

Increased allocation times Signup and view all the answers

What is a limitation of the stack?

It has a limited size Signup and view all the answers

Why is stack frame access easier than heap frame access?

Because the stack has small regions of memory and is cache friendly Signup and view all the answers

When should you allocate memory on the heap?

When you need to allocate a large block of memory and keep that variable around a long time Signup and view all the answers

What is the difference between stack and heap in terms of memory size allotment?

Heap is flexible and stack is not Signup and view all the answers

What happens when you use the new operator to allocate memory in C++?

Both the stack and the heap are utilized Signup and view all the answers

What is the default state of the integer allocated on the heap using the new operator?

Uninitialized, meaning it could contain any arbitrary value Signup and view all the answers

What is stored on the stack when you issue the command `int *ptr = new int;`?

The pointer variable <code>ptr</code> Signup and view all the answers

Why is memory allocation on the heap not automatically managed?

Because it must be explicitly freed by the programmer using <code>delete</code> Signup and view all the answers

What is the main difference in terms of access time between the stack and the heap?

Accessing time of heap takes more than a stack Signup and view all the answers

What is the first step in the provided code for deleting an element by value?

Check if the list is empty Signup and view all the answers

What happens if we don't have a destructor in the LinkedList class?

A memory leak occurs Signup and view all the answers

What is the purpose of checking if the element to be deleted is located at the start of the linked list?

To handle a special case of deletion Signup and view all the answers

What is the function of the 'next' variable in the provided code?

It points to the node after the node being deleted Signup and view all the answers

What is the consequence of not deleting the node being pointed to by the 'temp' variable?

A memory leak occurs Signup and view all the answers

Why is dynamic memory allocation used to create nodes in the LinkedList class?

To allow for flexibility in node creation Signup and view all the answers

What is the purpose of the increment function?

To increment the value of a variable passed by reference Signup and view all the answers

In the insert_before_node function, what happens if the element is found at the first node?

The new node is inserted before the head node Signup and view all the answers

What is the purpose of the temp variable in the insert_before_node function?

To traverse the linked list Signup and view all the answers

What happens if the element is not found in the linked list?

The new node is inserted at the end of the list Signup and view all the answers

How does the insert_before_node function insert a new node before a given node?

By updating the next pointer of the new node and the given node Signup and view all the answers

What is the condition for the while loop to stop executing in the insert_before_node function?

When temp->next becomes NULL Signup and view all the answers

What happens to the head node when a new node is inserted before it?

The head node is updated to point to the new node Signup and view all the answers

What is the purpose of the new_node variable in the insert_before_node function?

To create a new node with the given data Signup and view all the answers

Study Notes

Data Structures

Priority Queue: a queue where each element has a priority, and elements are served based on their priority
- Used in scenarios where elements need to be processed based on their importance or urgency (e.g. job scheduling, event handling, graph algorithms like Dijkstra's shortest path algorithm)
Double-ended Queue (Deque): a generalized version of a queue where elements can be inserted or removed from both ends
- Supports operations like push_front, push_back, pop_front, and pop_back
- Used in scenarios where elements need to be added or removed from both ends (e.g. sliding window algorithms, undo/redo operations, breadth-first search algorithms)
Tree: a hierarchical data structure consisting of nodes connected by edges
- Has a root node, and each node can have zero or more child nodes
- Common operations include insertion, deletion, and traversal (pre-order, in-order, post-order)
- Used in scenarios where data needs to be organized hierarchically (e.g. file systems, decision trees, binary search trees, heaps)

Stack and Heap Memory Allocation

Stack Allocation:
- Allocation happens on contiguous blocks of memory
- Memory size is known to the compiler, and memory is allocated on the stack when a function is called
- Stack frame access is easier and more cache-friendly compared to heap frames
- Stack is not flexible, and memory size cannot be changed
Heap Allocation:
- Allocation happens on the heap when using the new operator
- Memory allocated on the heap is not automatically managed and must be explicitly freed by the programmer using delete
- Memory allocated on the heap remains allocated until explicitly de-allocated
- Useful for situations where the amount of memory required cannot be determined at compile time (e.g. handling user input, working with data structures like linked lists, managing large data sets)

When to Use the Heap?

Use the heap when:
- You need to allocate a large block of memory (e.g. a large array or big class) and keep it around for a long time
- You need to dynamically allocate memory for situations where the amount of memory required cannot be determined at compile time
Use the stack when:
- You are dealing with relatively small variables that only need to persist as long as the function using them is alive

Disadvantages of Heap Memory

Performance Overhead:
- Slower allocation and de-allocation compared to the stack
- Fragmentation can lead to inefficient memory usage and increased allocation times
Fragmentation:
- Over time, the heap can become fragmented as blocks of memory are allocated and de-allocated in varying sizes

LinkedList Implementation

Insertion:
- If the element after which we want to insert a new node is located at the first node of the list, we simply set the next variable of the newly inserted node to point to the head and then set the value of head as the new_node
- If the list is not NULL and the element is not found at the first node, we create a new pointer variable temp and assign the head variable to it
- We traverse through the linked list using a while loop until temp->next becomes NULL
- If the item is found, the temp->next variable will not be NULL
Deletion:
- We first check if the list is empty
- If the element to be deleted is located at the start of the linked list, we delete it by setting the head to the next variable of the first node
- If the element is not found at the first index, we iterate through the linked list and check if the value of the node being iterated is equal to the value to be deleted
- If the comparison returns true, we set the next variable of the previous node to the node which exists after the node which is being deleted
Destructor:
- Essential for proper memory management
- Without a destructor, the allocated memory for the nodes would not be freed, resulting in a memory leak

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Description

Learn about two essential data structures: Priority Queue and Double-ended Queue. Understand their applications and operations.