Delete a given Node when a node is given.(0(1) solution)

Problem Overview

The LeetCode problem "Delete Node in a Linked List" is an interesting one that challenges our understanding of linked list operations at a more intricate level. Though the task description might seem straightforward, it tests the grasp of direct manipulation within a linked list without the help of helper structures.

Problem Statement

You are given a non-tail node of a singly linked list, and you task is to delete this node from the linked list. You will not be given access to the head of the list, so the problem essentially asks you to orchestrate a deletion from the middle of the list with only access to the node to be deleted.

Constraints:

• The node to be deleted is not the tail node, and it is guaranteed to be a valid node in the linked list.

Understanding the Problem

When traditional deletion in a linked list happens, we generally traverse the list, find the node before the target node, and reassign its next pointer to skip over the node to be deleted. However, in this instance, we can't do that since we don't have access to the node preceding the target.

Instead, we take an atypical approach by not genuinely deleting the target node but rather overwriting it with the next one, effectively bypassing the node marked for deletion.

Key DSA Concepts and Theory

1. Singly Linked List:

A singly linked list consists of nodes connected sequentially where each node stores data and has a pointer (or reference) to the next node in the sequence. The primary operations include insertion, deletion, traversal, and search.

2. Node Structure:

Each node in a singly linked list typically comprises:

• A data element
• A pointer to the next node

3. In-place Operations:

An in-place operation modifies data structures without the need for additional data structures. This problem inherently demands an in-place operation since we only need adjustments within the nodes, not any auxiliary storage.

Solution Approach

The primary idea here is to copy the data from the next node to the current node and then delete the next node. This shifts the content instead of true deletion.

Step-by-Step Solution Approach:

1. Copy Data: Copy the data from the next node into the current node.
2. Bypass Next Node: Redirect the current node's next pointer to next node's next.

This approach gives an illusion that the node was deleted as it no longer exists in the sequence of its former position.

Code Implementation

C++:

struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

void deleteNode(ListNode* node) {
    if (node == NULL || node->next == NULL) return; // Edge case, shouldn't occur here

    ListNode* nextNode = node->next;
    node->val = nextNode->val; // Copy the data
    node->next = nextNode->next; // Bypass the nextNode
    delete nextNode; // Free memory
}

Java:

class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}

public void deleteNode(ListNode node) {
    if (node == null || node.next == null) return; // Edge case, shouldn't occur here

    node.val = node.next.val; // Copy the data
    node.next = node.next.next; // Bypass the nextNode
}

Time and Space Complexity Analysis

• Time Complexity: O(1), because the operation involves a constant number of steps regardless of the list size.
• Space Complexity: O(1), since no extra data structures are utilized.

Common Mistakes to Avoid

• Attempting Direct Deletion: Remember that direct deletion isn’t possible; move the data instead.
• Ignoring Edge Cases: Though the node given isn't the tail, ensure code robustness by checks (even if redundant for this problem's constraints).

Similar Problems on Leetcode

• Reverse Linked List (#206)
• Remove Linked List Elements (#203)
• Swap Nodes in Pairs (#24)

Additional Resources and References

• GeeksforGeeks - Linked List Introduction
• Wikipedia - Linked List

This problem highlights an important aspect of algorithm design: sometimes, the solution isn't straightforward, and thinking creatively within constraints offered is crucial. Understanding basic linked list operations prepares one for more complex manipulations like this unique problem scenario.