Remove Duplicates from Sorted List II

class Solution:
    def deleteDuplicates(self, head: Optional[ListNode]) -> Optional[ListNode]:
        # Create a dummy node to make handling edge cases easier
        dummy = ListNode(0) = head
        prev = dummy

        while head:
            # Check if the current node has a duplicate value
            if and head.val ==
                # Skip all nodes with the same value
                while and head.val ==
                    head =
                # Connect the previous node to the node after the duplicates
                # If no duplicates, move the previous pointer to the current node
                prev =
            head =


10 Prerequisite LeetCode Problems

This involves manipulating linked lists and handling duplicates. Here are 10 simpler problems to prepare for this problem:

  1. Basic Linked List Manipulation

  2. Removal in Linked List

  3. Duplicates in Linked List

  4. Advanced Linked List Manipulation

  5. Merging and Sorting Linked List

These cover linked list manipulation, handling duplicates, and more complex operations like reversing and sorting, which are helpful for solving “Remove Duplicates from Sorted List II”.

Clarification Questions

Here are some potential clarification questions that could be asked about this problem:

  • Should the returned list contain any duplicate values or be fully unique?

  • If multiple duplicate nodes exist, do we remove all of them except the first instance or the last instance?

  • Can we assume the input list is non-empty?

  • Do we need to preserve the original nodes and pointers or can we destructively modify the input?

  • Should the relative order between non-duplicate nodes remain the same before and after removal?

  • Does the space complexity matter or can we use additional data structures?

  • Can we sort the entire final list again or does it need to maintain original order?

  • What should be done in the case of a cyclic list with duplicates?

  • Are there constraints on the range or distribution of node values we can assume?

  • Should the time complexity be optimized in any particular way?

Asking questions like these would help clarify ambiguous requirements, illuminate edge cases, and uncover hidden assumptions. This enables designing a more optimal, robust and efficient solution within the problem constraints.

Problem Analysis and Key Insights

Here are some key insights gained from analyzing the problem statement:

  • Operating on a linked list suggests using techniques like fast/slow pointers for traversal.

  • Requirement to remove duplicates indicates the need to track or identify repeated values.

  • Maintaining original sorted order means nodes can’t simply be rearranged arbitrarily.

  • In-place mutation requirement rules out approaches that store nodes externally.

  • Sorted order allows optimization like only forward traversal since duplicates must be adjacent.

  • Can leverage existing sorting structure to avoid having to re-sort afterward.

  • Small discrete integer value range allows compression or hashing techniques.

  • Can likely use nested traversal - outer list order preservation along with inner duplicate removal.

Overall, the insights around linked list traversal, leveraging the sorted property, nested approaches separating deduplication from ordering, and in-place mutation will help narrow down an optimal solution fitting the constraints.

Problem Boundary

Based on the problem statement and analysis, the scope of this problem is:

  • Input space - A sorted linked list of integer values from -100 to 100

  • Output - The same list with duplicate values removed

  • Rules - Must remove all duplicate nodes, preserve ascending sorted order

  • Objective - Deduplicate in-place, no full re-sorting needed

  • Non-goals - Implementing own linked list, sorting algorithms, optimal space/time complexity

So in summary, the scope is limited to:

  • Operating on an existing sorted linked list input

  • Applying in-place deduplication transformations

  • Maintaining the relative ordering of remaining nodes

  • Not concerned with creation/sorting logic or performance

The focus is on correctly applying linked list deduplication techniques given an ideal sorted input, rather than writing efficient sorting logic or optimizing complexities.

Here are some ways we can establish boundaries for this problem:


  • Existing sorted linked list of integer values
  • No constraints on size besides 0-300 nodes
  • Values limited to -100 to 100 range


  • Must remove duplicate valued nodes
  • Relative order of remaining nodes must be maintained
  • Modifications done in-place on original list


  • Return mutated input list
  • No other return values needed


  • No specific time or space complexity constraints specified


  • Input list state is self-contained
  • Results do not need to be persisted or stored

So in summary, the fixed input format, restricted transformations, minimal output, and lack of performance criteria define clear boundaries. The scope includes only in-place deduplication of a sorted linked list while maintaining ordering.

Problem Classification

This problem involves removing duplicate nodes from a sorted linked list. It falls under the domain of linked lists and algorithms.

The key ‘What’ components are:

  • A sorted input linked list
  • Nodes contain integer values
  • Removing any duplicate valued nodes
  • Maintaining the ascending sorted order
  • Returning the deduplicated sorted list

Based on these aspects, we can categorize this problem as:

  • Linked lists - involves manipulating pointer references between nodes
  • Deduplication - removing duplicate elements
  • Sorting - preserving ascending ordering
  • In-place modification - mutating existing input

So in summary, this is a linked list deduplication problem with the constraints of operating in-place while maintaining the sort order. It relies on concepts from linked data structures, sorting, and in-place transformations to mutate the input list. The core challenge is efficiently deduplicating while preserving order.

Distilling the Problem to Its Core Elements

This problem is based on the fundamental concepts of linked data structures and transforming ordered sequences.

At its core, it involves removing duplicate elements from a sorted list. I would describe it simply as:

“Given a sorted linked list, remove duplicate values while keeping the order.”

The core problem is deduplicating the list. We can simplify it to:

“Deduplicate a sorted linked list in-place.”

The key components are:

  • The input sorted linked list
  • Identifying duplicate elements
  • Removing the duplicates
  • Maintaining original order

The minimum operations are:

  • Traverse the list node-by-node
  • Check each node’s value against previous
  • For duplicates, remove node by updating pointers
  • Return mutated list

So in essence, this focuses on applying in-place deduplication techniques to a linked data structure while preserving its ordering, rather than sorting or performance optimizations.

Visual Model of the Problem

Here are some ways we could visualize this problem statement:

  • Show a simple linked list with duplicate values highlighted in red. Indicate removal by crossing out nodes.

  • Animate traversing the list, comparing values, and removing duplicates by redirecting pointers.

  • Use a diagram showing node values with arrows indicating order and duplicates in red. Show before and after transformation.

  • Visualize invalid scenarios like removing non-duplicates or scrambling order.

  • Use a flow chart to demonstrate key steps - traverse list, compare values, remove duplicates, maintain order, return list.

  • Provide small example lists visualized as grids showing values. Highlight duplicates and cross out removed nodes.

  • Leverage list visualization libraries to animate the traversal and transformation interactively.

  • Use color coding to indicate value ranges and mark duplicates/removals.

The goal is to leverage visual metaphors like animations, diagrams and examples to build intuition around traversing, transforming and maintaining linked list order. Highlighting the impact of removals is key.

Problem Restatement

Here’s how I would paraphrase the problem statement in my own words:

We’re given a linked list where the nodes are sorted in ascending order numerically. Our goal is to remove any nodes that have a value duplicated elsewhere in the list. However, we need to do this in-place without altering the original sorted relative order of the remaining non-duplicate nodes.

For example, if the input is [1, 2, 3, 3, 4, 4, 5], we would remove the second 3 and second 4 so that the final output is [1, 2, 5].

The key points are:

  • The list is sorted, we can’t fully rearrange nodes
  • We need to remove duplicates, keeping only first/last instances
  • Only duplicate nodes should be removed
  • Output order for non-duplicates must match input order

So in essence, we have to traverse the sorted list, selectively removing duplicates based on value, while maintaining the overall ascending order by preserving non-duplicate node positions.

Does this help summarize the core problem and constraints? Let me know if I’m missing or misunderstanding any key points.

Abstract Representation of the Problem

Here is one way to formulate an abstract representation of this problem:

Let’s define:

  • S = A sequence of numbered elements

  • D = The duplication function that identifies duplicate elements in S

  • R = The removal function that takes S and set of duplicates D and removes those elements

  • O = An ordering function that imposes a particular sequential ordering on S

Then the problem can be modeled as:


  • Sequence S
  • Duplication identification function D
  • Removal function R
  • Existing ordering function O


  • D to S to get set of duplicates
  • R to remove duplicates from S
  • Maintaining ordering O on S


  • Sequence S with duplicates removed per R while maintaining order O

This frames the problem as transforming an ordered sequence by applying duplication detection and removal logic while preserving the existing sequence order.

The key aspects are identifying duplicates, selectively removing them, and maintaining order on the sequence. Please let me know if you would modify or clarify this abstraction.


Here are some key terms and concepts relevant to this problem:

Linked List - Linear data structure made of nodes storing values and pointer links. Core data structure.

Node - Element of a linked list containing value and pointer(s).

Pointer - Reference to another node used to link nodes in order. Used to traverse and mutate list.

In-place - Modifying the existing input data structure itself, rather than copies. Required to mutate given list.

Sorted - Stored in a particular ascending or descending order. Enables assumptions about structure.

Duplicate - An element occurring more than once. Need to identify these.

Traversal - Visiting each element systematically. Required to inspect all nodes.

Relative Order - Original ordering between elements. Must be maintained for non-duplicates.

The key concepts center around linked list traversal, in-place mutation via pointers, and maintaining existing sort order - all while removing only duplicated elements. The terminology and properties influence the approach.

Problem Simplification and Explanation

Here’s one way I can explain this problem in simpler terms:

Key Concepts:

  • Linked List - The input data structure containing a chain of nodes

  • Duplicates - Multiple nodes store the same value

  • Removal - Taking out the duplicate nodes from the list

  • Sorted Order - Nodes are arranged numerically from low to high

  • Relative Order - The overall low-to-high sequence must be maintained


Imagine a sorted library catalog where multiple entries exist for some book titles. We need to tidy up the catalog by removing the duplicate entries, but keeping the remaining books in the original alphabetical order.

Specifically, we traverse the catalog, find any duplicates book titles based on value, cross them out, but maintain the overall sorted order by only removing the duplicates.

Similar to how we deduplicate the catalog in-place by selectively removing duplicate entries without reordering the other books.

Does this help explain the key concepts and constraints? Let me know if another analogy or simplification would be clearer!


Here are some characteristics of the problem that we can potentially leverage:

  • Sorted list order - We can traverse sequentially and only look forward for duplicates as values must be adjacent.

  • Small discrete value range - The -100 to 100 range allows optimization like hashing or bit encoding values.

  • Input list is self-contained - We can modify it in-place without needing to restore state later.

  • Output requires no particular format - We only need a working deduplicated list, not any metadata.

  • Duplicates are global - If a value appears again later, the first instance can be removed rather than last.

  • No specific time/space constraints - Simpler, non-optimized solutions may be acceptable depending on input size.

  • Mutable list nodes - We can directly rearrange pointers to remove nodes without copying data.

  • Relative order requirements - Actual index positions of non-duplicates must remain unchanged.

These properties allow us to optimize based on order, do in-place changes, leverage value locality and ignore output formatting or performance. The ability to mutate pointer references in particular facilitates efficient in-place deduplication.

Here are some key insights gained by analyzing the constraints:

  • Sorted order allows only forward traversal rather than bidirectional.

  • Small value range enables bitmapping or hash encodings for efficient value comparisons.

  • In-place mutation simplifies logic by allowing directly modifying existing nodes.

  • Output formatting relaxation allows focusing just on deduplication logic.

  • Global duplicates enable further optimizations like removing first instances.

  • No performance constraints means simpler algorithms are likely sufficient.

  • Pointer mutability provides efficient way to remove nodes without copying/rebuilding list.

  • Relative order requirements mean directly manipulating node positions when removing duplicates.

Overall, these constraints allow simplifying the implementation and scope to focus on logic for identifying duplicates and correctly mutating references to remove them while maintaining key ordering invariants. Optimizations leveraging ordering, value locality and direct manipulation help streamline the solution.

Case Analysis

Here are some additional test cases covering different aspects:

  1. Simple case

Input: [1, 2, 3, 3, 4, 4, 5]
Output: [1, 2, 5]

Analysis: Basic example with adjacent duplicates removed.

  1. Duplicates at ends

Input: [2, 3, 4, 4, 5, 5] Output: [2, 3]

Analysis: Checks endpoints properly handled.

  1. No duplicates

Input: [1, 2, 3] Output: [1, 2, 3]

Analysis: Handles lists with no duplicates present.

  1. Entirely duplicates

Input: [1, 1, 1] Output: [1]

Analysis: Validates logic when all nodes are duplicates.

  1. Empty list

Input: [] Output: []

Analysis: Handles empty list edge case.

Edge cases:

  • Empty list
  • Single node list
  • No duplicates present
  • All duplicates

The key aspects tested are duplicate removal, ordering preservation, and edge conditions. Boundary cases help validate correctness.

Here are some ideas for visualizing these test cases:

  • Draw linked lists with nodes in boxes showing values. Highlight duplicates in red.

  • Show traversal and pointer manipulation steps by animating or annotating diagrams.

  • Cross out duplicate nodes that get removed and rearrange arrows to show new pointer connections.

  • Before/after diagrams with duplicates removed and order maintained.

  • Explicitly highlight order is unchanged by annotating original index positions.

  • Contrast valid removals keeping order vs incorrectly scrambling non-duplicates.

  • Edge case lists like empty, single node, no duplicates, all duplicates shown simply.

  • Color code nodes from lowest to highest value to make order visual.

  • Leverage linked list visualization libraries for interactive animated examples.

  • Keep diagrams small and focused on highlighting aspects like duplicates and order.

The goal is to vividly convey node relationships, traversal order, duplicate identification and removal, and order preservation using minimal carefully annotated diagrams.

Here are some key insights gained from analyzing these test cases:

  • Simple examples are crucial baseline validation of core logic and assumptions.

  • Edge cases like empty or single node lists reveal assumptions about minimum viable lists.

  • Duplicates at endpoints check boundary logic is robust.

  • No duplicates case verifies unneeded changes are avoided.

  • All duplicates stresses duplication logic in isolation.

  • Order invariants need explicit visual validation in diagrams.

  • Animations or annotations help illustrate pointer manipulation steps.

  • Contrasting valid and invalid transformations clarifies expected behavior.

  • Small, focused examples are key for understanding complex pointer manipulation.

Overall, these cases validate logic across range from simple to edge cases, and illustrate side effects. Order visualization is essential. Targeted minimal examples simplify complex linked list mutation concepts.

Identification of Applicable Theoretical Concepts

Here are some mathematical and algorithmic concepts that could help solve this problem:

  • Fast/slow pointers - Can leapfrog along list to help identify duplicates and manipulate pointers for removal.

  • Hash tables - Allow quick lookup of values to check duplicates in O(1) time.

  • Bitmasking - Can compress node values into bit vectors for memory savings.

  • In-place algorithms - Linked lists support in-place mutation without copying/rebuilding.

  • Graph theory - Linked structure can be modeled as graph, leveraging graph algorithms.

  • Sorting algorithms - Maintaining relative order draws parallels to stable sorting.

  • Amortized analysis - Helps reason about cost of repeated duplicate removals spread over sequence.

  • Mutable data types - Linked list node pointers allow direct in-place manipulation.

Concepts from data structures, algorithms, bit manipulation, sorting, and graphs provide useful techniques for tracking state, complexity analysis, modeling the list, and safely mutating it.

Simple Explanation

Here’s how I would explain this problem in simple non-technical terms:

Imagine you have a sorted list of numbers, like a high score list that goes from lowest to highest scores. Some players have the same score listed multiple times.

We want to tidy up the list by removing any duplicate scores, but keeping the other scores in the original lowest-to-highest order.

For example, if the scores were:

[10, 15, 15, 20, 20, 30]

We would remove the extra 15 and 20 scores to end up with:

[10, 15, 30]

The order of the remaining scores stays the same, but any duplicates are taken out.

It’s like tidying up a sorted contact list by removing duplicate entries, without completely reordering the remaining names.

We scan through, compare adjacent entries, cross out duplicates, but maintain the overall sorted order by only selectively removing the duplicate values.

Problem Breakdown and Solution Methodology

Here is a step-by-step explanation of how I would approach solving this problem:

  1. Set previous node pointer to head

Keeps reference to previous node while traversing.

  1. Traverse list starting from head->next
  • Check if current value is equal to previous
  • If so, duplicate found
  1. Remove duplicate node:
  • Set previous->next to current->next
  • Bypass duplicate by pointing previous to node after
  1. Advance previous pointer

Move previous to current node after removal.

  1. Repeat steps 2-4 until end

Traverse entire list checking each node.

  1. Return head

Modified list now has duplicates removed.

For example on input [1, 2, 3, 3, 4, 4, 5]:

  1. prev = head
  2. current = 2, duplicate not found
  3. prev = 2
  4. current = 3
  5. current = 3, duplicate found
  6. prev->next = 4, removing duplicate
  7. prev = 4
  8. current = 4, duplicate found
  9. prev->next = 5, removing duplicate
  10. Return head

This shows the iterative traversal, duplicate checking, and pointer manipulation to remove nodes while maintaining order. Visualizing it is key.

For singly linked lists, we’d need to track previous value rather than node. Linked list types or duplicate scenarios would change logic slightly.

Inference of Problem-Solving Approach from the Problem Statement

Here are some key terms and how they guide my approach:

  • Linked List - Indicates using a linked node-based data structure and pointer manipulation.

  • Duplicate nodes - Checking for duplicate values requires comparable data types and tracking visited values.

  • Sorted order - Means traversal can be sequential rather than random access, simplifying logic.

  • In-place - Requires mutating existing nodes by updating pointers rather than copying data.

  • Remove nodes - Pointers must be directly manipulated to eliminate nodes and patch links.

  • Maintain order - Relative positions of non-duplicates must be preserved, can’t simply reorder all nodes.

  • Traversal - Iterative node-by-node processing required to inspect each element.

The core linked list, pointer manipulation, in-place mutation, and order maintenance concepts lead towards:

  • Traversal via pointers to support in-place changes
  • Comparing values and duplications checks
  • Careful pointer patching to remove nodes
  • Preserving pointer structure for non-duplicates

The keywords guide the incremental linked list traversal, duplicate tracking, and seamless node removal while limiting side effects.

We can visualize some key properties and aspects of this problem using tables and diagrams:

Linked List Structure:

Node - Value - Next

A - 1 - B B - 2 - C
C - 3 - D D - 3 - E E - 4 - F

  • Show basic linked list notation with node letters, values, and next pointers

Duplicate Nodes:

Node - Value - Next

A - 1 - B B - 2 - C C - 3 - D D - 3 - E E - 4 - F

  • Highlight, color, or otherwise visually distinguish duplicates

In-Place Mutation:

A - 1 - B B - 2 - C
C - 3 - F E - 4 - F

  • Show pointer manipulation by redirecting arrows when removing nodes

Preserving Order:

A - 1 - B // 0 B - 2 - C // 1
C - 3 - F // 2 E - 4 - F // 3

  • Annotate original index or position to highlight order stays the same

These diagrams help illustrate key aspects - the structure, duplicates, in-place changes, order preservation - in an accessible visual way.

How did you infer from the problem statement that this problem can be solved using ?

Simple Explanation of the Proof

I’m having trouble understanding the proof of this algorithm. Could you explain it in a way that’s easy to understand?

Stepwise Refinement

Here is one way to break this problem down into more granular steps:

High-level approach:

  1. Traverse linked list
  2. Remove duplicates
  3. Maintain order

Refined steps:

  1. Initialize previous and current pointers

  2. Loop through list:

  • Check if current value matches previous

  • If duplicate found:

    • Update previous->next pointer

    • Remove current node

  • Advance pointers

  1. Return head

Independent parts:

  • Pointer initialization
  • Traversal loop
  • Duplicate detection
  • Node removal
  • Pointer advancement

Repeatable patterns:

  • Comparing current vs previous values
  • Manipulating next pointers on duplicates
  • Advancing pointers forward

This breaks the problem down into pointer initialization, controlled traversal, modular duplicate handling, and safe pointer updates. The node manipulation patterns are reusable.

Solution Approach and Analysis

Here is a step-by-step explanation of how I would approach solving this problem:

  1. Initialize current and previous pointers

curr = head prev = None

  1. Loop through list
  • Set prev = curr
  • Move curr to next node
  1. Check for duplicate
  • If curr->val == prev->val
    • duplicate found
  1. Remove node
  • prev->next = curr->next
    • Bypass curr node
  1. Advance pointers
  • curr = prev->next
  • prev = prev->next
  1. Return head

For example on list:


  1. curr = A, prev = None

  2. curr = B, prev = A

  3. curr->val == prev->val duplicate B found

  4. prev->next = curr->next

  5. curr = C, prev = A

  6. Return A

The key is incrementally traversing with two pointers to enable safe in-place removal. Animations or drawings could help illustrate the steps clearly.

Identify Invariant

An invariant in this problem is a condition or statement that remains true throughout the execution of the solution. Some potential invariants are:

  • The input linked list structure and values remain unchanged. The original list is not mutated.

  • The relative order of non-duplicate nodes stays the same. Their relative positioning does not change.

  • A duplicate node once removed stays removed.

  • The sorting criteria of ascending node values is consistent. The notions of order and duplicates do not change.

  • The output list contains the same non-duplicate nodes as the input. Only redundant nodes are eliminated.

  • Once a node is checked for duplicates, it is not checked again. Each node is visited once.

So in essence, invariants are:

  • Original linked list is unchanged

  • Relative order of non-duplicates stays the same

  • Duplicate removal is permanent

  • Sorting criteria does not change

  • Non-duplicates remain in output list

The transformations cannot modify these structures and guarantees that define the problem throughout processing.

Identify Loop Invariant

What is the loop invariant in this problem?

Thought Process

Here is how I would think through solving this problem step-by-step:

The problem statement cues:

  • Linked list suggests node-by-node traversal through pointer connections

  • Removing duplicates indicates comparing node values to detect repeats

  • Maintaining sorted order means directly manipulating node positions is risky

So the steps would be:

  1. Initialize two pointers prev and curr for traversal

  2. Loop through list:

    • Check if curr node value equals prev node

    • If duplicate found:

      • Update prev->next pointer to skip curr node

      • Remove curr node from list

    • Advance prev and curr pointers forward

  3. Return head pointer to new list

In Python:

def removeDuplicates(head):

  curr = head
  prev = None
  while curr:
    if curr.val == prev.val:
      curr =
      prev = curr
      curr =
  return head

This uses dual pointers to traverse, check duplicates, and safely patch pointers to remove nodes while skipping malformed areas of list.

Here is one way to implement a solution in Python to remove duplicates from a sorted linked list:

class Solution:

    def deleteDuplicates(self, head: Optional[ListNode]) -> Optional[ListNode]:
        curr = head
        prev = None
        while curr:
            if prev and curr.val == prev.val:
                prev = curr
            curr =
        return head

The key steps are:

  • Initialize prev and curr pointers
  • Loop through list
  • Check curr vs prev node values
  • If duplicate, patch prev->next to remove curr node
  • Advance pointers forward

This uses the two pointers to traverse and safely eliminate duplicates by modifying pointers alone. The list order is maintained by skipping duplicate nodes.

Clude generates buggy code.

Establishing Preconditions and Postconditions

  1. Parameters:

    • What are the inputs to the method?
    • What types are these parameters?
    • What do these parameters represent in the context of the problem?
  2. Preconditions:

    • Before this method is called, what must be true about the state of the program or the values of the parameters?
    • Are there any constraints on the input parameters?
    • Is there a specific state that the program or some part of it must be in?
  3. Method Functionality:

    • What is this method expected to do?
    • How does it interact with the inputs and the current state of the program?
  4. Postconditions:

    • After the method has been called and has returned, what is now true about the state of the program or the values of the parameters?
    • What does the return value represent or indicate?
    • What side effects, if any, does the method have?
  5. Error Handling:

    • How does the method respond if the preconditions are not met?
    • Does it throw an exception, return a special value, or do something else?

Problem Decomposition

  1. Problem Understanding:

    • Can you explain the problem in your own words? What are the key components and requirements?
  2. Initial Breakdown:

    • Start by identifying the major parts or stages of the problem. How can you break the problem into several broad subproblems?
  3. Subproblem Refinement:

    • For each subproblem identified, ask yourself if it can be further broken down. What are the smaller tasks that need to be done to solve each subproblem?
  4. Task Identification:

    • Within these smaller tasks, are there any that are repeated or very similar? Could these be generalized into a single, reusable task?
  5. Task Abstraction:

    • For each task you’ve identified, is it abstracted enough to be clear and reusable, but still makes sense in the context of the problem?
  6. Method Naming:

    • Can you give each task a simple, descriptive name that makes its purpose clear?
  7. Subproblem Interactions:

    • How do these subproblems or tasks interact with each other? In what order do they need to be performed? Are there any dependencies?

From Brute Force to Optimal Solution

Here is a brute force approach and how we can optimize it:

Brute force:

  1. Make a copy of the linked list
  2. Iterate over the copy removing duplicates
  3. Re-sort the list
  4. Return the sorted copy

This liberally makes copies and fully re-sorts the list after duplicate removal.

Complexity: Time: O(NlogN) for sorting Space: O(N) for copying


  1. Traverse without making copy

Do in-place duplicate removal on original list.

Complexity: Time: O(N) Space: O(1)

  1. Maintain pointer references

Rather than swapping node positions, carefully update pointers to eliminate nodes.

Complexity: Time: O(N)
Space: O(1)

  1. No full re-sort needed

Preserve original relative order by skipping duplicate nodes.

Complexity: Time: O(N) Space: O(1)

  1. Track previous node

Allows safely unlinking current node when duplicate found.

Complexity: Time: O(N)
Space: O(1)

In summary, we optimized from making full copies and resorting to in-place manipulation with tight pointer control to maintain existing order. This improved time from O(NlogN) to O(N) and reduced space from O(N) to O(1).

Code Explanation and Design Decisions

  1. Identify the initial parameters and explain their significance in the context of the problem statement or the solution domain.

  2. Discuss the primary loop or iteration over the input data. What does each iteration represent in terms of the problem you’re trying to solve? How does the iteration advance or contribute to the solution?

  3. If there are conditions or branches within the loop, what do these conditions signify? Explain the logical reasoning behind the branching in the context of the problem’s constraints or requirements.

  4. If there are updates or modifications to parameters within the loop, clarify why these changes are necessary. How do these modifications reflect changes in the state of the solution or the constraints of the problem?

  5. Describe any invariant that’s maintained throughout the code, and explain how it helps meet the problem’s constraints or objectives.

  6. Discuss the significance of the final output in relation to the problem statement or solution domain. What does it represent and how does it satisfy the problem’s requirements?

Remember, the focus here is not to explain what the code does on a syntactic level, but to communicate the intent and rationale behind the code in the context of the problem being solved.

Coding Constructs

Consider the following piece of complex software code.

  1. What are the high-level problem-solving strategies or techniques being used by this code?

  2. If you had to explain the purpose of this code to a non-programmer, what would you say?

  3. Can you identify the logical elements or constructs used in this code, independent of any programming language?

  4. Could you describe the algorithmic approach used by this code in plain English?

  5. What are the key steps or operations this code is performing on the input data, and why?

  6. Can you identify the algorithmic patterns or strategies used by this code, irrespective of the specific programming language syntax?

Language Agnostic Coding Drills

Your mission is to deconstruct this code into the smallest possible learning units, each corresponding to a separate coding concept. Consider these concepts as unique coding drills that can be individually implemented and later assembled into the final solution.

  1. Dissect the code and identify each distinct concept it contains. Remember, this process should be language-agnostic and generally applicable to most modern programming languages.

  2. Once you’ve identified these coding concepts or drills, list them out in order of increasing difficulty. Provide a brief description of each concept and why it is classified at its particular difficulty level.

  3. Next, describe the problem-solving approach that would lead from the problem statement to the final solution. Think about how each of these coding drills contributes to the overall solution. Elucidate the step-by-step process involved in using these drills to solve the problem. Please refrain from writing any actual code; we’re focusing on understanding the process and strategy.

Targeted Drills in Python

Now that you’ve identified and ordered the coding concepts from a complex software code in the previous exercise, let’s focus on creating Python-based coding drills for each of those concepts.

  1. Begin by writing a separate piece of Python code that encapsulates each identified concept. These individual drills should illustrate how to implement each concept in Python. Please ensure that these are suitable even for those with a basic understanding of Python.

  2. In addition to the general concepts, identify and write coding drills for any problem-specific concepts that might be needed to create a solution. Describe why these drills are essential for our problem.

  3. Once all drills have been coded, describe how these pieces can be integrated together in the right order to solve the initial problem. Each drill should contribute to building up to the final solution.

Remember, the goal is to not only to write these drills but also to ensure that they can be cohesively assembled into one comprehensive solution.


Similar Problems

Here are 10 related LeetCode problems and why they are similar:

  1. Remove Duplicates from Sorted Array - In-place array mutation maintaining order.

  2. Partition List - Break list into two parts based on value, maintaining structure.

  3. Odd Even Linked List - Maintain relative ordering of odd/even nodes.

  4. Delete Node in a Linked List - Careful in-place pointer manipulation.

  5. Reverse Linked List - Pointer manipulation while preserving values.

  6. Merge Two Sorted Lists - Combine lists maintaining sorted order.

  7. Insertion Sort List - Mutate links to incrementally insert node in order.

  8. Sort List - Linked list sorting by modifying node pointers.

  9. Plus One Linked List - Traverse and increment list representing number.

  10. Rotate List - Manipulate pointers to rotate while maintaining connectivity.

The common themes are linked list traversal, in-place pointer manipulation, maintaining relative ordering, and removing elements based on constraints.