# Data Structures GCSE Resources

## GCSE Computer Science: Data Structures

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#### What is the difference between an array and a linked list?

An array is a data structure that stores a collection of elements of the same data type in a contiguous block of memory, while a linked list is a data structure that consists of a series of nodes, each containing a value and a pointer to the next node in the list. Arrays provide random access to elements, meaning that each element can be accessed directly using its index, while linked lists are better suited for dynamic data structures and efficient for inserting and deleting elements at any position.

#### What are the advantages of using a stack data structure?

Stacks are useful for maintaining the state of a program, such as keeping track of the function calls or undoing a series of operations. They are also used in algorithms such as depth-first search, where the last node visited is the first to be visited again. Stacks provide LIFO (Last-In-First-Out) ordering, which means that the most recently added element is the first to be removed.

#### What is a tree data structure, and what are some common applications of trees?

A tree is a hierarchical data structure consisting of nodes connected by edges. Each node can have zero or more child nodes. Trees are commonly used to represent hierarchical relationships between elements, such as the organization of a company or the structure of a file system. Trees are also used in many algorithms, such as binary search trees and decision trees.

#### How do data structures affect the efficiency of a program?

The choice of data structure can have a significant impact on the efficiency of a program. Some data structures are more efficient than others for particular operations, and the choice of data structure can depend on the size and complexity of the data being manipulated. For example, an array is efficient for random access to elements, but may not be the best choice for inserting or deleting elements in the middle of the array.

#### What is a hash table, and how does it work?

A hash table is a data structure that provides constant time average-case performance for inserting, searching, and deleting elements. It works by using a hash function to map keys to an index in an array. Each element is stored in a bucket at the corresponding index. When searching for an element, the hash function is used again to determine the index of the bucket containing the element. Hash tables are commonly used in applications such as database indexing and implementing associative arrays.