Question

Write a function ListNode *ListConcat(ListNode *list1, ListNode *list2) That concatenates the items in list2 to the end of list1 and returns the resulting list.

Short answer

Answer: To implement the 'ListConcat' function, follow these steps: 1. Check if any list is empty. If list1 is empty, return list2; if list2 is empty, return list1; if both are empty, return an empty list. 2. Iterate through list1 using a temporary pointer until you reach the last node. 3. Connect the last node of list1 to the first node of list2 by assigning the 'next' pointer of the last node of list1 to the first node of list2. 4. Return list1, which now contains all the nodes from both list1 and list2. The final function should resemble the following: ```cpp ListNode *ListConcat(ListNode *list1, ListNode *list2) { if (!list1) { return list2; } if (!list2) { return list1; } ListNode *temp = list1; while (temp->next) { temp = temp->next; } temp->next = list2; return list1; } ```

Step-by-step solution

Check if any list is empty

If list1 is empty, then we simply return list2, as there is nothing to concatenate. If list2 is empty, we just return list1. If both lists are empty, we return an empty list as well. Here's the code snippet for this step: ```cpp if (!list1) { return list2; } if (!list2) { return list1; } ```

Iterate through list1 to find the last node

We need to find the last node in list1 to attach list2 at the end. We will iterate through list1 using a temporary pointer until we reach the last node. Here's the code snippet for this step: ```cpp ListNode *temp = list1; while (temp->next) { temp = temp->next; } ```

Connect the last node of list1 with the first node of list2

Now that we have the last node of list1 in the 'temp' pointer, we can connect it with the first node of list2. We simply assign the 'next' pointer of the last node of list1 to the first node of list2. Here's the code snippet for this step: ```cpp temp->next = list2; ```

Return the concatenated list

Finally, we return list1, which now contains all the nodes from both list1 and list2. Here's the code snippet for this step: ```cpp return list1; ``` Now, combining all these steps, the final function 'ListConcat' will look like this: ```cpp ListNode *ListConcat(ListNode *list1, ListNode *list2) { // Step 1: Check if any list is empty if (!list1) { return list2; } if (!list2) { return list1; } // Step 2: Iterate through list1 to find the last node ListNode *temp = list1; while (temp->next) { temp = temp->next; } // Step 3: Connect the last node of list1 with the first node of list2 temp->next = list2; // Step 4: Return the concatenated list return list1; } ```

Key concepts

C++ programming

C++ is a highly versatile and powerful programming language which combines the features of both high-level and low-level languages. It is used to develop software where performance, efficiency, and control over system resources are critical.

In C++, developers can leverage a broad range of features including object-oriented programming, generic programming through templates, and low-level memory manipulation. This makes it suitable for developing operating systems, game engines, and high-performance applications. To solve problems in C++, one should understand its syntax, how to structure code using functions, and the proper use of data structures such as arrays, classes, and linked lists, which bring us to the exercise at hand: concatenating linked lists. Understanding how to manipulate such data structures in C++ is vital, as it forms the backbone of many complex algorithms and systems.

Linked List

A linked list is a foundational data structure in computer science, often used due to its efficient insertion and deletion operations compared to arrays. It is a collection of nodes, where each node contains data and a pointer to the next node in the sequence.

In the context of the exercise, a linked list allows us to store an ordered sequence of elements without the limitation of a fixed size. When concatenating two lists, the end of the first list is linked to the beginning of the second list. The crucial advantage of linked lists over arrays in this context is that the concatenation operation can be performed in O(1) time if the end of the first list is known, by simply adjusting pointers.

Function Implementation

Implementing functions is a core aspect of modular programming in C++. Functions are blocks of code that perform specific tasks and can be reused throughout a program. The exercise demonstrates a function named ListConcat designed to concatenate two linked lists.

The function returns a pointer to the resulting list. Key elements of function implementation include defining the function's return type, its parameters, the function body which contains the necessary logic, and the return statement. For example, robust error checking is vital, as in step 1 of the solution, which ensures the function behaves correctly even with empty lists.

Pointers in C++

Pointers are a critical feature of C++, providing a direct memory address reference to values stored in memory. They are especially powerful when working with dynamic data structures like linked lists, where they are used to keep track of node connections.

In the given exercise, pointers are essential to link the last node of list1 to the first node of list2. The use of a temporary pointer, temp, allows us to traverse the list and perform necessary operations without losing the reference to the head of the list. Proper understanding and management of pointers are crucial to avoid common errors like memory leaks and segmentation faults.