Скачать или смотреть Understanding the Python Linked List Data Structure in Leetcode

Confused about the `Python linked list` data structure in Leetcode? This blog explains how linked lists work, clarifying common misunderstandings using examples and diagrams.
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Understanding the Python Linked List Data Structure in Leetcode

If you are tackling problem-solving on Leetcode, specifically involving linked lists in Python, you might find yourself confused by how these data structures work and interact. One common point of confusion is around the ListNode structure used in many Python problems. Questions like, "Why does changing one variable sometimes affect the whole list while other times it does not?" are not uncommon for beginners. In this post, we will break down the concept of linked lists in Python, clarify their structures, and illustrate how different types of operations affect them.

What is a Linked List?

A linked list is a linear data structure where elements, known as nodes, are stored in sequential order. Each node contains:

Data: The value the node holds (in our case, typically an integer).

Pointer or Reference: A pointer to the next node in the sequence.

This structure allows efficient insertions and deletions compared to arrays since you don’t need to shift elements in memory.

The ListNode Class

In Leetcode, a linked list is commonly represented as follows:

[[See Video to Reveal this Text or Code Snippet]]

This means that each ListNode object can be thought of as storing one value (val) and a pointer to the next value in the list (next).

Exploring the Linked List Structure

Let's understand the linked list you've created with three nodes: 1, 2, and 3.

Visual Representation

You can visualize your linked list structured like this:

[[See Video to Reveal this Text or Code Snippet]]

Where a, b, and c are instances of the ListNode class.

Nodes and Pointers

When you instantiate the linked list in your code:

[[See Video to Reveal this Text or Code Snippet]]

You are effectively linking a to b and b to c.

Investigating Your Confusion

Changes and Their Impact

Now, let’s clarify your specific scenario. The confusion seems to lie in the difference between changing b.next and assigning b to None.

Setting b.next = None:

When you execute this command, you modify the next pointer of the node that b references:

[[See Video to Reveal this Text or Code Snippet]]

This shows that the linked list now ends with 2, effectively removing 3 from the sequence.

Setting b = None:

When you assign None to b, you are changing the reference of the variable b itself:

[[See Video to Reveal this Text or Code Snippet]]

The b variable no longer points to the ListNode that contains 2, but the underlying node is still part of the list linked to a. Thus, a.next still points to the node containing 2.

Summary of Key Differences

To summarize, here’s what you should keep in mind:

Modifying the next attribute directly affects the linked list by changing the connections between nodes.

Changing the variable reference (b in this case) does not affect the nodes themselves, just what your variable points to.

Conclusion

Understanding how linked lists operate in Python can simplify the process of solving problems on platforms like Leetcode. By recognizing the difference between direct changes to node pointers and variable reassignment, you'll enhance your problem-solving skills significantly.

We hope this explanation has cemented your understanding of the Python linked list data structure. Happy coding!