Question

The following table represents a portion of a linked list in a computer's main memory. Each entry in the list consists of two cells: The first contains a letter of the alphabet; the second contains a pointer to the next list entry. Alter the pointers so that the letter ' \(N\) ' is no longer in the list. Then replace the letter ' \(N\) ' with the letter ' \(G\) ' and alter the pointers so that the new letter appears in the list in its proper place in alphabetical order. $$ \begin{array}{cc} \text { Address } & \text { Contents } \\ 0 \times 30 & ' J \text { ' } \\ 0 \times 31 & 0 \times 38 \\ 0 \times 32 & ' B \text { ' } \\ 0 \times 33 & 0 \times 30 \\ 0 \times 34 & ' \times ' \\ 0 \times 35 & 0 \times 41 \\ 0 \times 36 & ' N \text { ' } \end{array} $$ $$ \begin{array}{cc} \text { Address } & \text { Contents } \\ 0 \times 37 & 0 \times 3 \mathrm{~A} \\ 0 \times 38 & ' \mathrm{~K} \text { ' } \\ 0 \times 39 & 0 \times 36 \\ 0 \times 3 \mathrm{~A} & ' \mathrm{P}^{\prime} \\ 0 \times 3 \mathrm{~B} & 0 \times 34 \end{array} $$

Short answer

Remove 'N', replace it with 'G', and update pointers so 'G' fits before 'J'.

Step-by-step solution

Identify 'N' and Adjust Pointers

The letter 'N' is located at address \(0 \times 36\). Its pointer, which is stored in \(0 \times 37\), points to \(0 \times 3A\). To remove 'N' from the list, find the address of the entry pointing to \(0 \times 36' and adjust its pointer to skip 'N'. From address \)0 \times 39\(, we change it from pointing to \)0 \times 36\( to point to \)0 \times 3A$, effectively removing 'N' from the list.

Replace 'N' with 'G'

Replace the letter at \(0 \times 36\) from 'N' to 'G'. This doesn't interfere with pointer logic itself but updates the data stored at that memory location.

Insert 'G' into Proper Alphabetical Order

To insert 'G' alphabetically, find the correct position. The current list order based on data is B (0x32), J (0x30), K (0x38), P (0x3A), X (0x34). 'G' comes before 'J', making it necessary to change the pointer at \(0 \times 33\) from \(0 \times 30\) to \(0 \times 36'. Finally, \)0 \times 37\( now points to \)0 \times 30$ to continue the list from 'G' to 'J'.

Key concepts

Linked List

In computer science, a linked list is a data structure consisting of a sequence of elements. Each element contains two parts: the data and a pointer. The pointer indicates the location of the next element. This structure allows for efficient insertion and removal of elements.

• Linked lists are dynamic, meaning they can grow or shrink as needed.
• They are particularly useful when frequent insertion and deletion of data items are required.
• The list can be traversed by following the pointers from one element to the next.

In our exercise, we manage a linked list containing letters of the alphabet. We perform operations to remove and replace elements by adjusting pointers, showcasing how linked lists allow for flexible data manipulation.

Pointers

Pointers are a fundamental concept in computer science, especially within data structures like linked lists. A pointer is essentially a variable that stores a memory address referencing another variable or data location.

• Pointers provide the means to navigate through data structures, such as a linked list.
• In linked lists, pointers are used to connect nodes, representing the links between them.
• Changing a pointer effectively alters the connection throughout the list, as seen when removing or inserting elements.

For instance, in the exercise, altering a pointer involves changing which memory address it points to, effectively skipping over a node or reordering the nodes.

Memory Addressing

Memory addressing refers to the method used by software to access data in computer memory. Each piece of data stored in memory has a specific address that can be used to locate it.

• Addresses are critical for tracking where data is stored in a linked list.
• The linked list in our problem uses hexadecimal addresses (e.g., 0x30, 0x36) to denote the position of each entry in memory.
• Proper memory addressing ensures data integrity and structure within the linked list.

In our context, understanding the memory addresses helps us correctly adjust pointers to remove and reorder nodes without data loss.

Alphabetical Order

Alphabetical order involves arranging items in the sequence they would appear in an alphabetical index. It is intuitive for human understanding and reliable for systematic data structuring.

• In a linked list, maintaining alphabetical order often requires adjusting pointers to correctly position elements as they are inserted.
• This exercise demonstrates inserting a new element ('G') in its correct place by comparing it to existing elements.
• Correct alphabetical ordering maintains data organization, making it easy to search and traverse.

Our task involves adjusting the list so that the new letter follows the alphabetical sequence of existing entries, requiring careful pointer management.

Data Manipulation

Data manipulation is the process of adjusting data to convert or organize it in a desired format. In linked lists, data manipulation involves directly changing the data or the connections between data elements to achieve specific goals.

• Common operations include insertion, deletion, and reordering data within the list.
• In our task, 'N' is removed, and 'G' is inserted, requiring precise pointer adjustments.
• This demonstrates how linked lists are flexible, allowing efficient changes to data structure with direct manipulation.

The exercise provides practical insights into how pointers and memory addressing facilitate data manipulation, highlighting the adaptability of linked lists.