Data Structure Unit 2: Array Overview

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Questions and Answers

What is the primary advantage of using arrays in programming?

Arrays are dynamically sized.

Arrays require less memory than other data structures.

Arrays can store elements of different data types.

Arrays provide random access lookup time. (correct)

How is a one-dimensional array typically accessed?

By using multiple indices.

By random memory addresses.

By calculating half the size of the array.

By a single subscript index. (correct)

Which of the following array types allows elements to be organized in rows and columns?

Dynamic array.

Multi-dimensional array. (correct)

Sparse array.

One-dimensional array.

What is the correct syntax for declaring an array in C?

array_name[array_size] = {elements}; Signup and view all the answers

In a two-dimensional array, how is an element accessed?

array_name[m][n]; Signup and view all the answers

What does the 'bucket' in array representation refer to?

A section of memory allocated for each element. Signup and view all the answers

What is a characteristic of a one-dimensional array?

It stores elements in sequential order. Signup and view all the answers

What is a characteristic of a multi-dimensional array?

It allows for accessing elements using multiple indices. Signup and view all the answers

Which operation is NOT one of the basic operations performed on an array?

Seek Signup and view all the answers

What will happen when an element is inserted in the middle of an array?

Elements after the insertion point will be shifted to accommodate the new element. Signup and view all the answers

What is the output of the given C program after inserting elements?

LA[0] = 2, LA[1] = 3, LA[2] = 4 Signup and view all the answers

What is the result of a sequential search?

It may return True or False regarding the item’s presence. Signup and view all the answers

How is a three-dimensional array typically defined in terms of its size?

It can hold elements based on the product of its three dimensions. Signup and view all the answers

What must be done to an array in C before inserting a new element?

Sufficient memory space must be allocated. Signup and view all the answers

What is the main characteristic of the items in a sequential search that affects its efficiency?

Items are placed randomly in the list. Signup and view all the answers

How many comparisons does a sequential search require in the worst-case scenario when the item is present?

n comparisons Signup and view all the answers

What can be inferred about the average case in a sequential search when an item is present?

We find it with approximately n/2 comparisons. Signup and view all the answers

What happens to the searching process in a sequential search if the list of items is sorted in ascending order?

The search can stop early if an item is larger than the target. Signup and view all the answers

What is the time complexity of the sequential search algorithm as the number of items increases?

O(n) Signup and view all the answers

In what scenario would a sequential search require the most comparisons to determine an item is not present?

When all items are compared. Signup and view all the answers

Which searching technique is preferred when the data set is organized?

Binary search Signup and view all the answers

What is the initial value of LOC when beginning a linear search for an item?

1 Signup and view all the answers

In a linear search, what happens when the item to be searched is not found in the array?

LOC is set to 0. Signup and view all the answers

How does the binary search algorithm determine the next segment to search?

It checks if the item is greater or less than the middle element. Signup and view all the answers

When performing a binary search, what condition must be met before continuing the loop?

BEG ≤ END and DATA[MID] ≠ ITEM. Signup and view all the answers

What is the primary prerequisite for using a binary search algorithm?

The array must be sorted in increasing order. Signup and view all the answers

In the context of the linear search algorithm, what does the variable N represent?

The length of the array. Signup and view all the answers

What is one of the main characteristics of the sorting operation?

Rearranges data into a defined sequence. Signup and view all the answers

What is the purpose of the MID variable in a binary search?

To determine the midpoint of the current search range. Signup and view all the answers

Which of the following best describes a linear search's processing method?

Tests each element sequentially until the item is found. Signup and view all the answers

What is a key distinguishing feature of the calloc() function compared to malloc()?

calloc() initializes each allocated block to a default value of 0. Signup and view all the answers

Which line of code correctly allocates memory for 20 integers using calloc()?

ptr = (int*)calloc(20, sizeof(int)); Signup and view all the answers

What is the purpose of the free() function in C?

To de-allocate previously allocated memory. Signup and view all the answers

What happens to the memory when realloc() is called?

It maintains the existing values and allocates new memory. Signup and view all the answers

Which statement is true about garbage collection in programming languages?

It automatically detects and frees memory that is no longer needed. Signup and view all the answers

In which case would a memory leak most likely occur?

When realloc() is called without freeing existing memory. Signup and view all the answers

What is a potential consequence of failing to free dynamically allocated memory in C?

Memory fragmentation leading to reduced system performance. Signup and view all the answers

What does the term 'dangling pointer' refer to in C?

A pointer that points to a memory location that has been freed. Signup and view all the answers

What is a critical difference between C and garbage-collected languages?

In C, programmers must manually manage memory allocation and deallocation. Signup and view all the answers

What does the realloc() function allow you to achieve?

It changes the size of already allocated memory space. Signup and view all the answers

Study Notes

Array Overview

An array is a collection of items of the same data type stored in contiguous memory locations.
Allows easier calculation of positions through offsets using the base memory location of the first element.

Syntax for Creating Arrays

C/C++ syntax: data_type array_name[array_size] = {elements separated using commas}; or data_type array_name[array_size];

Need for Arrays

Useful for solving varied problems from simple sorting to complex issues like the traveling salesperson problem.
Advantageous due to random access lookup time.

Array Representation

Represented as buckets indexed from 0 to n-1, where n is the size of the array.
In a 2D array, indexed as array_name[m][n], with each dimension having its own size.

Types of Arrays

One-Dimensional Array: Accessed sequentially using a single index.
Multi-Dimensional Array: Contains multiple dimensions, such as 2D or 3D arrays, accessed through row and column indices.

Basic Operations on Arrays

Traverse: Loop through the array to perform operations.
Insertion: Adding a new element at a given index.
Deletion: Removing an element from a specified index.
Search: Finding an element by value or index.
Update: Modifying an element at a specific index.

Inserting New Elements

New elements can be inserted if there’s enough allocated memory.
Elements may need to shift forward to maintain order.

Searching Algorithms

Searching allows retrieval of specific items from a set, critical for data structures.

Sequential Search (Linear Search)

Searches each item in sequential order, returning the index if found, otherwise -1.
Time Complexity: O(n) where n is the number of elements, with cases:
- Best: 1 comparison if found at the start.
- Worst: n comparisons if searched at the end or not found.
- Average: n/2 comparisons.

Binary Search

Used on sorted arrays to efficiently find an item.
Time Complexity: O(log n) due to halving the search space.
Searches based on comparison of the target item with the middle element.

Sorting

Sorting arranges data either in ascending or descending order.
Essential for efficient searching and retrieval of information.

Data Structure: Linked List

A linked list is a linear data structure made up of nodes, where each node contains data and a reference to the next node.
Easier insertion and deletion of elements compared to array-based data structures.
Commonly used as the underlying structure for stacks, queues, and associative arrays.
Nodes consist of a data field and a link or pointer to the next node.
The first node is termed the "head," while the last node can refer to the "tail" or link back to the head in circular lists.

Types of Linked Lists

Singly Linked List: Each node contains a data field and a single link to the next node.
Doubly Linked List: Nodes have two links; one points to the next node while the other points to the previous node, facilitating bidirectional traversal.
Circular Linked List: The last node's link points back to the first node, allowing continuous traversal without a null reference.
Doubly Circular Linked List: Similar to doubly linked lists but with circular connections at both ends.

Operations on Linked Lists

Traversing: Accessing each element only once; implemented using a pointer that moves through nodes using the link information.
Searching:
- Unsorted List: Sequentially access each node until the desired element is found, which can be time-consuming.
- Sorted List: Start from the head and compare until an element larger than the target is found, reducing the number of comparisons.
Inserting:
- At the beginning, using a pointer to update head and links accordingly.
- At a specific location, with checks for null conditions and memory availability.
- In a sorted list while maintaining the order.
Deleting:
- First Node: Simply update the head pointer and free the old node.
- Last Node: Traverse to the end node, update links, and free memory.
- Specific Node: Traverse, updating previous links to bypass the targeted node, deleting it afterward.

Node Structure Representation

Singly Linked List:

struct node {
    int data;
    struct node *next;
};

Doubly Linked List:

struct node {
    int data;
    struct node *next;
    struct node *prev;
};

Memory Management in C

Dynamic memory allocation is crucial for linked lists due to the need for flexible sizes.
Functions include:
- malloc(): Allocates uninitialized memory.
- calloc(): Allocates memory and initializes it to zero.
- free(): Deallocates previously allocated memory.
- realloc(): Changes the size of previously allocated memory blocks.

Key Characteristics

Linked lists do not have a fixed size, allowing dynamic resizing.
They can easily expand without memory wastage, a significant advantage over arrays.
Traversal in linked lists is inherently linear and can be inefficient for searches compared to other data structures like trees or hash tables.

Applications

Frequently utilized in applications where the number of elements is unknown or changes frequently, such as:
- Implementing data structures like stacks and queues.
- Managing resources in systems where elements need to be added and removed frequently.### Dynamic Memory Allocation in C
Dynamic memory allocation allows changing the size of a data structure, like an array, during runtime.
Essential when the number of required elements varies, such as reducing size from 9 to 5 or increasing from 9 to 12.
Achieved using four key C library functions defined in the <stdlib.h> header.

Functions for Dynamic Memory Allocation

malloc()
- Stands for "memory allocation."
- Allocates a single block of memory with a specified size.
- Does not initialize memory, leaving it with garbage values.
- Syntax: ptr = (cast-type*) malloc(byte-size);
- Example: ptr = (int*) malloc(100 * sizeof(int)); (allocates 400 bytes for 100 integers).
calloc()
- Stands for "contiguous allocation."
- Allocates multiple blocks of memory and initializes them with zero.
- Syntax: ptr = (cast-type*) calloc(n, element-size);
- Example: ptr = (float*) calloc(25, sizeof(float)); (allocates space for 25 floats).
free()
- Used to deallocate memory allocated by malloc() or calloc().
- Helps to prevent memory wastage by freeing unused memory.
- Syntax: free(ptr);
realloc()
- Re-allocates memory that has already been allocated.
- If current allocation is insufficient, realloc() changes size while preserving existing values.
- New blocks initialized with garbage values.
- Syntax: ptr = realloc(ptr, newSize);

Garbage Collection

Garbage Collection (GC) is a feature found in languages like C# and Java.
Automatically frees memory allocated to unused objects through garbage collectors (GC engines).
Prevents memory overflow and frees developers from manual memory management.
Reduces memory-related bugs like memory leaks and dangling pointers.
Languages without GC (like C and C++) require manual memory management, increasing potential for errors.
GC algorithms identify and remove unneeded objects, reclaiming memory without affecting used ones.

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Description

Explore the fundamentals of arrays in data structures in this quiz from Unit 2. Understand how arrays store multiple items of the same type at contiguous memory locations, making it easier to calculate the position of each element. Test your knowledge on the definition, structure, and benefits of using arrays.