Linked List LeetCode Problems: All 75,
With Python Solutions

Every problem in this library that LeetCode tags Linked List. 63 of them carry a complete Python solution, a worked example and the time and space complexity of the approach.

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Easy: 12
Medium: 56
Hard: 7

1 pattern

How Linked List problems are solved

A tag names the subject, not the method. These pattern hubs cover the techniques that actually solve Linked List problems — each one explains the approach, gives a Python template and states its complexity.

Linked ListRewire pointers in place, with a dummy head and a saved next to keep it safe.

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python

Please analyze this context and help me answer the question or solve the problem.

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

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python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

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QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

Linked List problems by difficulty

Problems with a complete Python solution are listed first, then by ascending problem number.

Easy (12)

Easy problems
No.	Problem	Topics
0021	Merge Two Sorted Lists	Recursion, Linked List
0083	Remove Duplicates from Sorted List	Linked List
0141	Linked List Cycle	Hash Table, Linked List, Two Pointers
0160	Intersection of Two Linked Lists	Hash Table, Linked List, Two Pointers
0203	Remove Linked List Elements	Recursion, Linked List
0206	Reverse Linked List	Recursion, Linked List
0234	Palindrome Linked List	Stack, Recursion, Linked List +1
0705	Design HashSet	Design, Array, Hash Table +2
0706	Design HashMap	Design, Array, Hash Table +2
0876	Middle of the Linked List	Linked List, Two Pointers
1290	Convert Binary Number in a Linked List to Integer	Linked List, Math
1474	Delete N Nodes After M Nodes of a Linked ListPremium	Linked List

Medium (56)

Medium problems
No.	Problem	Topics
0002	Add Two Numbers	Recursion, Linked List, Math
0019	Remove Nth Node From End of List	Linked List, Two Pointers
0024	Swap Nodes in Pairs	Recursion, Linked List
0061	Rotate List	Linked List, Two Pointers
0082	Remove Duplicates from Sorted List II	Linked List, Two Pointers
0086	Partition List	Linked List, Two Pointers
0092	Reverse Linked List II	Linked List
0109	Convert Sorted List to Binary Search Tree	Tree, Binary Search Tree, Linked List +2
0114	Flatten Binary Tree to Linked List	Stack, Tree, Depth-First Search +2
0116	Populating Next Right Pointers in Each Node	Tree, Depth-First Search, Breadth-First Search +2
0117	Populating Next Right Pointers in Each Node II	Tree, Depth-First Search, Breadth-First Search +2
0138	Copy List with Random Pointer	Hash Table, Linked List
0142	Linked List Cycle II	Hash Table, Linked List, Two Pointers
0143	Reorder List	Stack, Recursion, Linked List +1
0146	LRU Cache	Design, Hash Table, Linked List +1
0147	Insertion Sort List	Linked List, Sorting
0148	Sort List	Linked List, Two Pointers, Divide and Conquer +2
0237	Delete Node in a Linked List	Linked List
0328	Odd Even Linked List	Linked List
0355	Design Twitter	Design, Hash Table, Linked List +1
0382	Linked List Random Node	Reservoir Sampling, Linked List, Math +1
0430	Flatten a Multilevel Doubly Linked List	Depth-First Search, Linked List, Doubly-Linked List
0445	Add Two Numbers II	Stack, Linked List, Math
0622	Design Circular Queue	Design, Queue, Array +1
0641	Design Circular Deque	Design, Queue, Array +1
0707	Design Linked List	Design, Linked List
0725	Split Linked List in Parts	Linked List
0817	Linked List Components	Array, Hash Table, Linked List
1019	Next Greater Node In Linked List	Stack, Array, Linked List +1
1171	Remove Zero Sum Consecutive Nodes from Linked List	Hash Table, Linked List
1367	Linked List in Binary Tree	Tree, Depth-First Search, Linked List +1
1472	Design Browser History	Stack, Design, Array +3
1669	Merge In Between Linked Lists	Linked List
1670	Design Front Middle Back Queue	Design, Queue, Array +2
1721	Swapping Nodes in a Linked List	Linked List, Two Pointers
1797	Design Authentication Manager	Design, Hash Table, Linked List +1
2058	Find the Minimum and Maximum Number of Nodes Between Critical Points	Linked List
2074	Reverse Nodes in Even Length Groups	Linked List
2095	Delete the Middle Node of a Linked List	Linked List, Two Pointers
2130	Maximum Twin Sum of a Linked List	Stack, Linked List, Two Pointers
2181	Merge Nodes in Between Zeros	Linked List, Simulation
2289	Steps to Make Array Non-decreasing	Stack, Array, Linked List +1
2326	Spiral Matrix IV	Array, Linked List, Matrix +1
2487	Remove Nodes From Linked List	Stack, Recursion, Linked List +1
2807	Insert Greatest Common Divisors in Linked List	Linked List, Math, Number Theory
2816	Double a Number Represented as a Linked List	Stack, Linked List, Math
0369	Plus One Linked ListPremium	Linked List, Math
0379	Design Phone DirectoryPremium	Design, Queue, Array +2
0426	Convert Binary Search Tree to Sorted Doubly Linked ListPremium	Stack, Tree, Depth-First Search +4
0708	Insert into a Sorted Circular Linked ListPremium	Linked List
1265	Print Immutable Linked List in ReversePremium	Stack, Recursion, Linked List +1
1634	Add Two Polynomials Represented as Linked ListsPremium	Linked List, Math, Two Pointers
1756	Design Most Recently Used QueuePremium	Design, Array, Linked List +3
1836	Remove Duplicates From an Unsorted Linked ListPremium	Hash Table, Linked List
2046	Sort Linked List Already Sorted Using Absolute ValuesPremium	Linked List, Two Pointers, Sorting
2674	Split a Circular Linked ListPremium	Linked List, Two Pointers

Hard (7)

Hard problems
No.	Problem	Topics
0023	Merge k Sorted Lists	Linked List, Divide and Conquer, Heap (Priority Queue) +1
0025	Reverse Nodes in k-Group	Recursion, Linked List
0432	All O`one Data Structure	Design, Hash Table, Linked List +1
0460	LFU Cache	Design, Hash Table, Linked List +1
1206	Design Skiplist	Design, Linked List
2296	Design a Text Editor	Stack, Design, Linked List +3
0716	Max StackPremium	Stack, Design, Linked List +2

How Linked List problems are solved

When the Linked List problem arrives live.

Approach

Approach

Approach

Linked List problems by difficulty

Easy (12)12

Medium (56)56

Hard (7)7

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Easy (12)

Medium (56)

Hard (7)