What is the time complexity of Delete Node in a Linked List?

The optimal solution has a time complexity of O(1).

What data structures are used to solve Delete Node in a Linked List?

This problem uses Linked List. Understanding these concepts is essential for solving this Medium problem efficiently.

What are the key insights for solving Delete Node in a Linked List?

Insight 1: Since we don't have access to the previous node, we can't simply re-link the 'next' pointer of the previous node to skip the node to be deleted. Insight 2: Because we can't directly remove the node, we can overwrite the node's value with the value of the next node and then remove the next node.

Which companies ask LeetCode 237. Delete Node in a Linked List in interviews?

This problem is frequently asked at Nvidia, Oracle, PayPal.

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Delete Node in a Linked List - LeetCode 237 Solution

Delete Node in a Linked List - Complete Solution Guide

Delete Node in a Linked List is LeetCode problem 237, a Medium level challenge. This complete guide provides step-by-step explanations, multiple solution approaches, and optimized code in python3, java, cpp, c.

Problem Statement

There is a singly-linked list head and we want to delete a node node in it. You are given the node to be deleted node . You will not be given access to the first node of head . All the values of the linked list are unique , and it is guaranteed that the given node node is not the last node in the linked list. Delete the given node. Note that by deleting the node, we do not mean removing it from memory. We mean: The value of the given node should not exist in the linked list. The number of nodes

Detailed Explanation

The problem asks us to delete a given node from a singly linked list. Crucially, we are *not* given the head of the list, only the node to be deleted. We also know that the given node is guaranteed not to be the last node in the list. The task is to effectively remove the given node from the linked list without having direct access to the nodes before it. By deleting, we mean modifying the linked list such that the deleted node's value is no longer present, the number of nodes is reduced by one, and the order of remaining nodes is preserved.

Solution Approach

The solution takes advantage of the fact that we are given the node to delete and that this node is not the tail. Instead of directly deleting the node, we overwrite the node's value with the value of its immediate successor. Then, we effectively remove the successor by updating the 'next' pointer of the current node to point to the node after the successor. This effectively deletes the *next* node, but achieves the goal of removing the value of the original node we wanted to delete.

Step-by-Step Algorithm

Step 1: Copy the value of the next node (node.next.val) into the current node (node.val).
Step 2: Update the 'next' pointer of the current node (node.next) to point to the node after the next node (node.next.next). This effectively removes the next node from the linked list.

Key Insights

Insight 1: Since we don't have access to the previous node, we can't simply re-link the 'next' pointer of the previous node to skip the node to be deleted.
Insight 2: Because we can't directly remove the node, we can overwrite the node's value with the value of the next node and then remove the next node.
Insight 3: The restriction that the node to be deleted is not the tail node is essential for this approach to work.

Complexity Analysis

Time Complexity: O(1)

Space Complexity: O(1)

Topics

This problem involves: Linked List.

Companies

Asked at: Nvidia, Oracle, PayPal.

Delete Node in a Linked List | LeetCode 237

Medium

Linked List

Time: O(1)Space: O(1)

Solution Code

Available in:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public void deleteNode(ListNode node) {
        node.val = node.next.val;
        node.next = node.next.next;
    }
}

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Problem Info

Description

Problem 237: Delete Node in a Linked List - Detailed explanation and solution approaches.

Topics

Linked List

Companies

NvidiaOraclePayPal

Stats

Difficulty:Medium

Languages:4

Companies:3

Problem #:237

Problem Explanation

💡

Think Before You Code

🤔 Ask Yourself

→What is the input? What output do I need?
→Can I solve a smaller version of this problem first?
→What patterns have I seen in similar problems?

✏️ Try This First

Before looking at the solution, try to solve it on paper with a simple example!

🚀 Try on LeetCode

Solution Approach

📋

Step-by-Step Solution

2 steps

1
Step 1: Copy the value of the next node (node.next.val) into the current node (node.val).
2
Step 2: Update the 'next' pointer of the current node (node.next) to point to the node after the next node (node.next.next). This effectively removes the next node from the linked list.

💡

Pro Tip for Students

Try tracing through each step with a small example on paper before coding. Understanding "why" each step happens is more important than memorizing the code!

⚡

Complexity Analysis

⏱️

Time Complexity

O(1)

⚡ Constant time - Super fast! Same speed regardless of input size.

💾

Space Complexity

O(1)

💪 Constant space - Uses same memory regardless of input!

📝

Why?

The algorithm involves only a constant number of operations: copying a value and updating a pointer. Therefore, the time complexity is constant, O(1). No additional memory is used, so the space complexity is also constant, O(1).

📖New to Big O? Click to learn more

Big O Notation - Quick Guide

O(1)Best - Instant

O(log n)Excellent - Binary Search

O(n)Good - One loop

O(n log n)OK - Sorting

O(n²)Slow - Nested loops

O(2ⁿ)Very Slow - Recursion

Alternative Approaches

Iterating from Head (If we had access to Head)

If we had access to the head of the linked list, we could iterate through the list until we find the node *before* the node to be deleted. Then, we could update the 'next' pointer of that previous node to skip the node to be deleted.

Time: O(n)Space: O(1)

Trade-offs: This approach requires access to the head of the linked list, which we don't have in the original problem. If we had the head, this would be a more 'standard' way to delete a node, but it's less efficient (O(n) vs O(1)).

✨

Key Insights

1Insight 1: Since we don't have access to the previous node, we can't simply re-link the 'next' pointer of the previous node to skip the node to be deleted.
2Insight 2: Because we can't directly remove the node, we can overwrite the node's value with the value of the next node and then remove the next node.
3Insight 3: The restriction that the node to be deleted is not the tail node is essential for this approach to work.

📚

Key Terms Explained

For Students

Linked List

Elements connected via pointers. Like a chain where each link knows the next.

Edge Cases

Edge case 1: Node to be deleted is the last node - This is explicitly excluded by the problem constraints. The solution wouldn't work because there's no next node to copy data from.
Edge case 2: Empty list or null node passed - The problem states the number of nodes is in the range [2, 1000] and the node to be deleted is in the list. Therefore, we do not need to handle empty lists or null nodes being passed into the function.

⚠️

Common Mistakes to Avoid

✗Common mistake 1: Trying to delete the node directly without copying the value from the next node. Since we don't have access to the previous node, a standard deletion is impossible.

✗Common mistake 2: Forgetting to update both the value and the next pointer. Only updating the value leaves the next node still in the list, and only updating the pointer leaves the old value in the list.

✅

Learning Tip

Every mistake is a learning opportunity! When you make an error, understand why it happened before moving on.

🌍

Where is This Used in Real Life?

💼Real-world scenario 1: Managing dynamic data structures in memory. This technique can be useful when you need to remove an element from a linked list-like structure quickly and you only have access to the node you want to 'remove'.

🏦Real-world scenario 2: Implementing undo/redo functionality. Linked lists are often used to track the history of actions, and efficient node removal is essential for a smooth user experience.

💡Understanding real-world applications helps you see the "why" behind algorithms. It's not just about passing interviews—these concepts power the apps and websites you use every day!

Author's Notes

💡 Key Insight

The dummy node technique prevents edge cases. For cycle detection, Floyd's algorithm is the standard. Always handle empty list and single node cases.

🎯 Interview Tip

Medium problems are the bread and butter of technical interviews. Practice explaining your approach before coding.

⚠️ Watch Out

Losing reference to nodes when modifying pointers. Use temporary variables to save references.

Written by Saswata Mondal

Software Engineer • Algorithms Enthusiast • Interview Coach

👨‍💻

About the Author

👨‍💻

Saswata MondalAuthor400+ LC Problems

B.Tech CSE, IEM Kolkata | LeetCode Rating: 1672 (Top 15%)

Certified: IBM Java Developer, NPTEL Programming in Java

Last updated: July 28, 2024LeetCode Profile GitHub

This solution has been crafted based on my experience solving 400+ LeetCode problems. Each explanation is designed to help you understand the underlying concepts, not just memorize the code.

Community Tips & Insights

I was asked this exact problem at my Google interview. The interviewer wanted me to optimize space complexity.

@InterviewProJul 14

Try solving this without using extra space first. It's a great exercise for understanding the underlying pattern.

@CodeNinjaJul 7

In a real interview, always clarify constraints first. Ask about input size and value ranges.

@TechLeadJun 30

❓

Frequently Asked Questions

How does the fast/slow pointer technique work?

Fast pointer moves 2 steps while slow moves 1 step. When fast reaches the end, slow is at middle. If there's a cycle, they will meet. This technique is used for: finding middle node, detecting cycles, finding cycle start point, and checking palindromes.

How much time should I spend on a medium problem in interviews?

In a 45-minute interview, aim for: 5-10 minutes understanding and clarifying, 5-10 minutes discussing approach, 20-25 minutes coding, and 5-10 minutes testing. If stuck after 15 minutes of thinking, verbalize your thought process and ask for hints.

What is the importance of time and space complexity analysis?

Complexity analysis is crucial because: 1) Interviewers always ask about it, 2) It helps you choose between approaches, 3) It demonstrates CS fundamentals. Always state both time and space complexity, and be prepared to explain how you derived them.

What is the optimal approach for "Delete Node in a Linked List"?

For this medium-level Linked List problem, the key is to identify the core pattern. Analyze the input constraints to determine acceptable time complexity. Consider whether standard techniques can optimize the solution. Always handle edge cases and validate your approach with examples before coding.

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