Array LeetCode Problems: All 1,569,
With Python Solutions

Every problem in this library that LeetCode tags Array. 1,332 of them carry a complete Python solution, a worked example and the time and space complexity of the approach.

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Easy: 330
Medium: 862
Hard: 377

Array problems by difficulty

Showing the first 200 of 1,569 problems. Problems with a complete Python solution are listed first, then by ascending problem number.

Easy (31)

Easy problems
No.	Problem	Topics
0001	Two Sum	Array, Hash Table
0014	Longest Common Prefix	Trie, Array, String
0026	Remove Duplicates from Sorted Array	Array, Two Pointers
0027	Remove Element	Array, Two Pointers
0035	Search Insert Position	Array, Binary Search
0066	Plus One	Array, Math
0088	Merge Sorted Array	Array, Two Pointers, Sorting
0108	Convert Sorted Array to Binary Search Tree	Tree, Binary Search Tree, Array +2
0118	Pascal's Triangle	Array, Dynamic Programming
0119	Pascal's Triangle II	Array, Dynamic Programming
0121	Best Time to Buy and Sell Stock	Array, Dynamic Programming
0136	Single Number	Bit Manipulation, Array
0169	Majority Element	Array, Hash Table, Divide and Conquer +2
0217	Contains Duplicate	Array, Hash Table, Sorting
0219	Contains Duplicate II	Array, Hash Table, Sliding Window
0228	Summary Ranges	Array
0268	Missing Number	Bit Manipulation, Array, Hash Table +3
0283	Move Zeroes	Array, Two Pointers
0303	Range Sum Query - Immutable	Design, Array, Prefix Sum
0349	Intersection of Two Arrays	Array, Hash Table, Two Pointers +2
0350	Intersection of Two Arrays II	Array, Hash Table, Two Pointers +2
0414	Third Maximum Number	Array, Sorting
0448	Find All Numbers Disappeared in an Array	Array, Hash Table
0455	Assign Cookies	Greedy, Array, Two Pointers +1
0463	Island Perimeter	Depth-First Search, Breadth-First Search, Array +1
0485	Max Consecutive Ones	Array
0495	Teemo Attacking	Array, Simulation
0496	Next Greater Element I	Stack, Array, Hash Table +1
0500	Keyboard Row	Array, Hash Table, String
0506	Relative Ranks	Array, Sorting, Heap (Priority Queue)
0561	Array Partition	Greedy, Array, Counting Sort +1

Medium (128)

Medium problems
No.	Problem	Topics
0011	Container With Most Water	Greedy, Array, Two Pointers
0015	3Sum	Array, Two Pointers, Sorting
0016	3Sum Closest	Array, Two Pointers, Sorting
0018	4Sum	Array, Two Pointers, Sorting
0031	Next Permutation	Array, Two Pointers
0033	Search in Rotated Sorted Array	Array, Binary Search
0034	Find First and Last Position of Element in Sorted Array	Array, Binary Search
0036	Valid Sudoku	Array, Hash Table, Matrix
0039	Combination Sum	Array, Backtracking
0040	Combination Sum II	Array, Backtracking
0045	Jump Game II	Greedy, Array, Dynamic Programming
0046	Permutations	Array, Backtracking
0047	Permutations II	Array, Backtracking, Sorting
0048	Rotate Image	Array, Math, Matrix
0049	Group Anagrams	Array, Hash Table, String +1
0053	Maximum Subarray	Array, Divide and Conquer, Dynamic Programming
0054	Spiral Matrix	Array, Matrix, Simulation
0055	Jump Game	Greedy, Array, Dynamic Programming
0056	Merge Intervals	Array, Sorting
0057	Insert Interval	Array
0059	Spiral Matrix II	Array, Matrix, Simulation
0063	Unique Paths II	Array, Dynamic Programming, Matrix
0064	Minimum Path Sum	Array, Dynamic Programming, Matrix
0073	Set Matrix Zeroes	Array, Hash Table, Matrix
0074	Search a 2D Matrix	Array, Binary Search, Matrix
0075	Sort Colors	Array, Two Pointers, Sorting
0078	Subsets	Bit Manipulation, Array, Backtracking
0079	Word Search	Depth-First Search, Array, String +2
0080	Remove Duplicates from Sorted Array II	Array, Two Pointers
0081	Search in Rotated Sorted Array II	Array, Binary Search
0090	Subsets II	Bit Manipulation, Array, Backtracking
0105	Construct Binary Tree from Preorder and Inorder Traversal	Tree, Array, Hash Table +2
0106	Construct Binary Tree from Inorder and Postorder Traversal	Tree, Array, Hash Table +2
0120	Triangle	Array, Dynamic Programming
0122	Best Time to Buy and Sell Stock II	Greedy, Array, Dynamic Programming
0128	Longest Consecutive Sequence	Union Find, Array, Hash Table
0130	Surrounded Regions	Depth-First Search, Breadth-First Search, Union Find +2
0134	Gas Station	Greedy, Array
0137	Single Number II	Bit Manipulation, Array
0139	Word Break	Trie, Memoization, Array +3
0150	Evaluate Reverse Polish Notation	Stack, Array, Math
0152	Maximum Product Subarray	Array, Dynamic Programming
0153	Find Minimum in Rotated Sorted Array	Array, Binary Search
0162	Find Peak Element	Array, Binary Search
0164	Maximum Gap	Array, Bucket Sort, Radix Sort +1
0167	Two Sum II - Input Array Is Sorted	Array, Two Pointers, Binary Search
0179	Largest Number	Greedy, Array, String +1
0189	Rotate Array	Array, Math, Two Pointers
0198	House Robber	Array, Dynamic Programming
0200	Number of Islands	Depth-First Search, Breadth-First Search, Union Find +2
0204	Count Primes	Array, Math, Enumeration +1
0209	Minimum Size Subarray Sum	Array, Binary Search, Prefix Sum +1
0213	House Robber II	Array, Dynamic Programming
0215	Kth Largest Element in an Array	Array, Divide and Conquer, Quickselect +2
0216	Combination Sum III	Array, Backtracking
0221	Maximal Square	Array, Dynamic Programming, Matrix
0229	Majority Element II	Array, Hash Table, Counting +1
0238	Product of Array Except Self	Array, Prefix Sum
0240	Search a 2D Matrix II	Array, Binary Search, Divide and Conquer +1
0260	Single Number III	Bit Manipulation, Array
0274	H-Index	Array, Counting Sort, Sorting
0275	H-Index II	Array, Binary Search
0284	Peeking Iterator	Design, Array, Iterator
0287	Find the Duplicate Number	Bit Manipulation, Array, Two Pointers +1
0289	Game of Life	Array, Matrix, Simulation
0300	Longest Increasing Subsequence	Array, Binary Search, Dynamic Programming
0304	Range Sum Query 2D - Immutable	Design, Array, Matrix +1
0307	Range Sum Query - Mutable	Design, Binary Indexed Tree, Segment Tree +2
0309	Best Time to Buy and Sell Stock with Cooldown	Array, Dynamic Programming
0313	Super Ugly Number	Array, Math, Dynamic Programming
0318	Maximum Product of Word Lengths	Bit Manipulation, Array, String
0322	Coin Change	Breadth-First Search, Array, Dynamic Programming
0324	Wiggle Sort II	Greedy, Array, Divide and Conquer +2
0334	Increasing Triplet Subsequence	Greedy, Array
0347	Top K Frequent Elements	Array, Hash Table, Divide and Conquer +5
0368	Largest Divisible Subset	Array, Math, Dynamic Programming +1
0373	Find K Pairs with Smallest Sums	Array, Heap (Priority Queue)
0376	Wiggle Subsequence	Greedy, Array, Dynamic Programming
0377	Combination Sum IV	Array, Dynamic Programming
0378	Kth Smallest Element in a Sorted Matrix	Array, Binary Search, Matrix +2
0380	Insert Delete GetRandom O(1)	Design, Array, Hash Table +2
0384	Shuffle an Array	Design, Array, Math +1
0393	UTF-8 Validation	Bit Manipulation, Array
0396	Rotate Function	Array, Math, Dynamic Programming
0399	Evaluate Division	Depth-First Search, Breadth-First Search, Union Find +4
0406	Queue Reconstruction by Height	Binary Indexed Tree, Segment Tree, Array +1
0413	Arithmetic Slices	Array, Dynamic Programming, Sliding Window
0416	Partition Equal Subset Sum	Array, Dynamic Programming
0417	Pacific Atlantic Water Flow	Depth-First Search, Breadth-First Search, Array +1
0419	Battleships in a Board	Depth-First Search, Array, Matrix
0421	Maximum XOR of Two Numbers in an Array	Bit Manipulation, Trie, Array +1
0427	Construct Quad Tree	Tree, Array, Divide and Conquer +1
0435	Non-overlapping Intervals	Greedy, Array, Dynamic Programming +1
0436	Find Right Interval	Array, Binary Search, Sorting
0442	Find All Duplicates in an Array	Array, Hash Table, Sorting
0447	Number of Boomerangs	Array, Hash Table, Math
0452	Minimum Number of Arrows to Burst Balloons	Greedy, Array, Sorting
0453	Minimum Moves to Equal Array Elements	Array, Math
0454	4Sum II	Array, Hash Table
0456	132 Pattern	Stack, Array, Binary Search +2
0457	Circular Array Loop	Array, Hash Table, Two Pointers
0462	Minimum Moves to Equal Array Elements II	Array, Math, Sorting
0473	Matchsticks to Square	Bit Manipulation, Array, Dynamic Programming +2
0474	Ones and Zeroes	Array, String, Dynamic Programming
0475	Heaters	Array, Two Pointers, Binary Search +1
0477	Total Hamming Distance	Bit Manipulation, Array, Math
0486	Predict the Winner	Recursion, Array, Math +2
0491	Non-decreasing Subsequences	Bit Manipulation, Array, Hash Table +1
0494	Target Sum	Array, Dynamic Programming, Backtracking
0497	Random Point in Non-overlapping Rectangles	Reservoir Sampling, Array, Math +4
0498	Diagonal Traverse	Array, Matrix, Simulation
0503	Next Greater Element II	Stack, Array, Monotonic Stack
0518	Coin Change II	Array, Dynamic Programming
0522	Longest Uncommon Subsequence II	Array, Hash Table, Two Pointers +2
0523	Continuous Subarray Sum	Array, Hash Table, Math +1
0524	Longest Word in Dictionary through Deleting	Array, Two Pointers, String +1
0525	Contiguous Array	Array, Hash Table, Prefix Sum
0526	Beautiful Arrangement	Bit Manipulation, Array, Dynamic Programming +2
0528	Random Pick with Weight	Array, Math, Binary Search +2
0529	Minesweeper	Depth-First Search, Breadth-First Search, Array +1
0532	K-diff Pairs in an Array	Array, Hash Table, Two Pointers +2
0539	Minimum Time Difference	Array, Math, String +1
0540	Single Element in a Sorted Array	Array, Binary Search
0542	01 Matrix	Breadth-First Search, Array, Dynamic Programming +1
0553	Optimal Division	Array, Math, Dynamic Programming
0554	Brick Wall	Array, Hash Table
0560	Subarray Sum Equals K	Array, Hash Table, Prefix Sum
0565	Array Nesting	Depth-First Search, Array

Hard (41)

Hard problems
No.	Problem	Topics
0004	Median of Two Sorted Arrays	Array, Binary Search, Divide and Conquer
0037	Sudoku Solver	Array, Hash Table, Backtracking +1
0041	First Missing Positive	Array, Hash Table
0042	Trapping Rain Water	Stack, Array, Two Pointers +2
0051	N-Queens	Array, Backtracking
0068	Text Justification	Array, String, Simulation
0084	Largest Rectangle in Histogram	Stack, Array, Monotonic Stack
0085	Maximal Rectangle	Stack, Array, Dynamic Programming +2
0123	Best Time to Buy and Sell Stock III	Array, Dynamic Programming
0135	Candy	Greedy, Array
0140	Word Break II	Trie, Memoization, Array +4
0149	Max Points on a Line	Geometry, Array, Hash Table +1
0154	Find Minimum in Rotated Sorted Array II	Array, Binary Search
0174	Dungeon Game	Array, Dynamic Programming, Matrix
0188	Best Time to Buy and Sell Stock IV	Array, Dynamic Programming
0212	Word Search II	Trie, Array, String +2
0218	The Skyline Problem	Binary Indexed Tree, Segment Tree, Array +5
0220	Contains Duplicate III	Array, Bucket Sort, Ordered Set +2
0239	Sliding Window Maximum	Queue, Array, Sliding Window +2
0312	Burst Balloons	Array, Dynamic Programming
0315	Count of Smaller Numbers After Self	Binary Indexed Tree, Segment Tree, Array +4
0321	Create Maximum Number	Stack, Greedy, Array +2
0327	Count of Range Sum	Binary Indexed Tree, Segment Tree, Array +4
0329	Longest Increasing Path in a Matrix	Depth-First Search, Breadth-First Search, Graph +5
0330	Patching Array	Greedy, Array
0335	Self Crossing	Geometry, Array, Math
0336	Palindrome Pairs	Trie, Array, Hash Table +1
0354	Russian Doll Envelopes	Array, Binary Search, Dynamic Programming +1
0363	Max Sum of Rectangle No Larger Than K	Array, Binary Search, Matrix +2
0381	Insert Delete GetRandom O(1) - Duplicates allowed	Design, Array, Hash Table +2
0391	Perfect Rectangle	Geometry, Array, Hash Table +2
0403	Frog Jump	Array, Dynamic Programming
0407	Trapping Rain Water II	Breadth-First Search, Array, Matrix +1
0410	Split Array Largest Sum	Greedy, Array, Binary Search +2
0446	Arithmetic Slices II - Subsequence	Array, Dynamic Programming
0472	Concatenated Words	Depth-First Search, Trie, Array +3
0480	Sliding Window Median	Array, Hash Table, Sliding Window +1
0493	Reverse Pairs	Binary Indexed Tree, Segment Tree, Array +4
0502	IPO	Greedy, Array, Sorting +1
0517	Super Washing Machines	Greedy, Array
0546	Remove Boxes	Memoization, Array, Dynamic Programming

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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.

Type your message...

GPT-6.1 Terra

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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

Primary display

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

Array problems by difficulty

Easy (31)31

Medium (128)128

Hard (41)41

When the Array problem arrives live.

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Easy (31)

Medium (128)

Hard (41)