CS 1112 Quiz 5: Data Structures and Abstractions in Java, Exams of Computer Science

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CS 1112 Quiz 5

COMPUTER SCIENCE

"What do we mean by "the list is an abstraction"? - CORRECT ANSWER This means that a list is a conceptual representation of a collection of elements, rather than a physical or tangible object. A list is a way of organizing and managing data that can be implemented in various ways using programming languages." "Contrast the space complexity of list operations in a linked list against list operations in an array based list. - CORRECT ANSWER In a linked list, the space complexity is linear to the number of nodes in the list. Each node requires additional memory to store the value and the pointers to the previous and next nodes. In an array based list, the space complexity is also linear to the number of elements in the list. However, in addition to the elements, an array-based list also requires additional memory to store the underlying array structure." "Justify why a while loop is recommended for iteration in a linked list instead of a for loop? - CORRECT ANSWER A while loop is recommended for iteration in a linked list instead of a for loop because a linked list does not have a fixed length that can be easily expressed as an index range. A while loop allows us to traverse" "What is an iterator? - CORRECT ANSWER An iterator is an object that enables the traversal of a data structure and access to its elements without exposing its underlying implementation." "How does using an iterator for iteration differ from indexed based iteration? - CORRECT ANSWER Using an iterator for iteration differs from indexed based iteration in that iterator-based iteration does not rely on index values to access elements, but instead uses a next() method to move through the elements of the data structure one by one. In contrast, indexed based iteration relies on accessing elements by their index position." "Why should iterator based iteration be used for linked lists over index based iteration? - CORRECT ANSWER Iterator based iteration should be used for linked lists over index based iteration because linked lists are not indexed-based data structures, meaning that accessing elements by their index position would require iterating through the list until the desired element is reached. This process can be inefficient and time-consuming, especially for large lists. In contrast, using an iterator allows for efficient traversal of a linked list, since it moves from one element to the next without the need to iterate through the entire list." "Why do we create abstraction layers? - CORRECT ANSWER Abstraction layers are used to simplify complex systems by breaking them down into smaller, more manageable components. Each layer provides a simplified interface to the layer below it, while hiding the internal workings of that layer. This can help to make systems more modular, flexible, and easier to maintain."

"Analyze the efficiency of remove for an linked-list based List. - CORRECT ANSWER Removing an element from a linked-list-based List has an average time complexity of O(1) if the element to be removed is known, or O(n) if the element must be searched for first. This is because removing an element from a linked list involves updating the next pointer of the previous node to skip over the removed node, which can be done in constant time. However, searching for the element to be removed takes linear time in the worst case." "What is the role of the head pointer in a linked-list? - CORRECT ANSWER The head pointer in a linked-list points to the first node in the list. It serves as the starting point for traversing the list and accessing its elements." "Define the structure of a singly-linked linked-list node? - CORRECT ANSWER A singly-linked linked-list node consists of two parts: a data field that stores the value of the element, and a next field that points to the next node in the list. The last node in the list has a null value for its next field, indicating the end of the list." "How is the end of a linked-list represented? - CORRECT ANSWER The end of a linked-list is represented by a null value in the next field of the last node in the list." "Assuming the maintenance of a tail pointer, why is appending to the tail end of a singly- linked linked-list constant time complexity? - CORRECT ANSWER If a tail pointer is maintained, appending to the tail end of a singly-linked linked-list can be done in constant time, O(1), because the tail pointer already points to the last node in the list. The new element can simply be added as a new node after the last node, and the tail pointer can be updated to point to the new node." "Assuming no tail pointer, why is appending to the tail end of a singly-linked linked-list linear time complexity? - CORRECT ANSWER If a tail pointer is not maintained, appending to the tail end of a singly-linked linked-list takes linear time, O(n), because the entire list must be traversed to find the last node in the list. Once the last node is found, a new node can be added after it to append the new element." "Is it necessary to maintain both a head and a tail pointer for a linked-list to support all List interactions? Justify your answer. - CORRECT ANSWER It is not necessary to maintain both a head and a tail pointer for a linked-list to support all List interactions. While a tail pointer can make certain operations, such as appending to the end of the list, more efficient, they can still be performed without a tail pointer. However, a head pointer is necessary to identify the beginning of the list and to support operations such as iterating over the elements in the list and accessing individual elements by their index." "Assess the feasibility of adding to the head of a singly-linked linked-list. If this operation is feasible, analyze the efficiency of adding to the head of a linked-list. - CORRECT ANSWER Adding to the head of a singly-linked linked-list is feasible and takes constant time, O(1). This is because a new node can be created with the new element and the

next pointer set to the current head node. Then, the head pointer can be updated to point to the new node, making it the new first element in the list." "Assess the feasibility of removing from the head of a singly-linked linked-list. If this operation is feasible, analyze the efficiency of removing from the head of a linked-list. - CORRECT ANSWER Removing from the head of a singly-linked linked-list is feasible and takes constant time, O(1). This is because the head pointer can simply be updated to point to the second node in the list, effectively removing the first node from the list." "Assess the feasibility of adding to the tail of a singly-linked linked-list. If this operation is feasible, analyze the efficiency of adding to the tail of a linked-list. - CORRECT ANSWER Adding to the tail of a singly-linked linked-list is feasible, but takes linear time, O(n), if a tail pointer is not maintained. This is because the entire list must be traversed to find the last node in the list, and a new node can then be added after it to append the new element. If a tail pointer is maintained, adding to the tail takes constant time, O(1), as explained in question 21." What are the characteristics of a list? - CORRECT ANSWER A list is an ordered collection of elements, where each element can be of any data type. The characteristics of a list include: Ordered: The elements in a list are ordered, meaning that each element has a specific position in the list. Mutable: Lists are mutable, meaning that they can be modified by adding, removing or changing elements. Dynamic: Lists can grow or shrink as elements are added or removed. Heterogeneous: A list can contain elements of different data types. Indexable: Each element in a list can be accessed using an index." "What do we mean by absolute position? - CORRECT ANSWER Absolute position refers to the specific location of an element within a list, based on its index or numerical position. For example, the first element in a list has an absolute position of 0, the second element has an absolute position of 1, and so on." "What do we mean by relative position? - CORRECT ANSWER Relative position refers to the location of an element within a list, relative to another element. For example, an element may be located two positions to the left or three positions to the right of another element in the list." "What is meant by the term interface? What is meant by interactions and behaviors? - CORRECT ANSWER An interface is a set of methods or functions that define how a user or other software component can interact with a program or system. Interactions refer to the ways in which users or components communicate with a system, while behaviors refer to the actions or responses of the system in response to those interactions."

"How can the tail end of a circular linked list be identified? - CORRECT ANSWER In a circular linked list, there is no true tail end since the last node points back to the head of the list. However, any node can be designated as the "tail" node for the purposes of adding or removing nodes from the end of the list. One way to do this is to maintain a tail pointer that points to the last node in the list." "Define the structure of a circular doubly-linked-list? - CORRECT ANSWER A circular doubly-linked list is a data structure that consists of a set of nodes, each of which contains three components: a value, a pointer to the previous node, and a pointer to the next node. In a circular doubly-linked list, the last node points back to the first node, forming a loop." "Analyze the efficiency of List interactions in a circular doubly-linked-list. - CORRECT ANSWER In a circular doubly-linked list, most List interactions have the same time complexity as in a doubly-linked list. Adding or removing nodes from either end of the list (head or tail) is constant time complexity O(1). Adding or removing nodes from an arbitrary position in the list is linear time complexity O(n/2) on average, where n is the size of the list. Iteration over the list is also linear time complexity O(n)." "Contrast the time complexity of list operations in a linked list against list operations in an array based list. - CORRECT ANSWER In a linked list, adding or removing nodes from either end of the list (head or tail) is constant time complexity O(1), while adding or removing nodes from an arbitrary position in the list is linear time complexity O(n/2) on average, where n is the size of the list. Iteration over the list is also linear time complexity O(n). In an array based list, adding or removing elements from the end of the list is constant time complexity O(1) on average (assuming no resizing is required), while adding or removing elements from an arbitrary position in the list is linear time complexity O(n), where n is the size of the list. Iteration over the list is also linear time complexity O(n)." "