LeetCode

My solutions to LeetCode problems in Java.

Structure

Every problem is a single test class in src/test/java/org/overmind, named after the problem:

• the Javadoc links to the problem and gives a short description;
• the tests are the examples from the problem statement;
• the solution is the nested Solution class (or the class the problem asks to design).

Shared helpers live in src/main/java/org/overmind: ListNode and TreeNode with ListNode.of(1, 2, 3) and TreeNode.of(3, 9, 20, null, null, 15, 7) factories that accept the LeetCode notation.

Running the tests

Requires JDK 25.

./gradlew test

Problems

97 of 220 problems solved: 47 easy, 42 medium, 8 hard. Unsolved problems are disabled test classes with a stub solution.

#	Problem	Difficulty	Solution	Solved
1	Two Sum	Easy	TwoSumTest	✅
2	Add Two Numbers	Medium	AddTwoNumbersTest	✅
3	Longest Substring Without Repeating Characters	Medium	LongestSubstringWithoutRepeatingCharactersTest	✅
4	Median of Two Sorted Arrays	Hard	MedianOfTwoSortedArraysTest	✅
5	Longest Palindromic Substring	Medium	LongestPalindromicSubstringTest	✅
6	Zigzag Conversion	Medium	ZigzagConversionTest	✅
7	Reverse Integer	Medium	ReverseIntegerTest	✅
8	String to Integer (atoi)	Medium	StringToIntegerAtoiTest	✅
9	Palindrome Number	Easy	PalindromeNumberTest	✅
10	Regular Expression Matching	Hard	RegularExpressionMatchingTest	✅
11	Container With Most Water	Medium	ContainerWithMostWaterTest	✅
12	Integer to Roman	Medium	IntegerToRomanTest	✅
13	Roman to Integer	Easy	RomanToIntegerTest	✅
14	Longest Common Prefix	Easy	LongestCommonPrefixTest	✅
15	3Sum	Medium	ThreeSumTest	✅
16	3Sum Closest	Medium	ThreeSumClosestTest	✅
17	Letter Combinations of a Phone Number	Medium	LetterCombinationsOfAPhoneNumberTest	✅
18	4Sum	Medium	FourSumTest	✅
19	Remove Nth Node From End of List	Medium	RemoveNthNodeFromEndOfListTest	✅
20	Valid Parentheses	Easy	ValidParenthesesTest	✅
21	Merge Two Sorted Lists	Easy	MergeTwoSortedListsTest	✅
22	Generate Parentheses	Medium	GenerateParenthesesTest	✅
23	Merge k Sorted Lists	Hard	MergeKSortedListsTest	✅
24	Swap Nodes in Pairs	Medium	SwapNodesInPairsTest	✅
25	Reverse Nodes in k-Group	Hard	ReverseKGroupTest	✅
26	Remove Duplicates from Sorted Array	Easy	RemoveDuplicatesFromSortedArrayTest	✅
27	Remove Element	Easy	RemoveElementTest	✅
28	Find the Index of the First Occurrence in a String	Easy	FindTheIndexOfTheFirstOccurrenceInAStringTest	✅
29	Divide Two Integers	Medium	DivideTwoIntegersTest	✅
30	Substring with Concatenation of All Words	Hard	SubstringWithConcatenationOfAllWordsTest
31	Next Permutation	Medium	NextPermutationTest	✅
32	Longest Valid Parentheses	Hard	LongestValidParenthesesTest
33	Search in Rotated Sorted Array	Medium	SearchInRotatedSortedArrayTest	✅
34	Find First and Last Position of Element in Sorted Array	Medium	FindFirstAndLastPositionOfElementInSortedArrayTest
35	Search Insert Position	Easy	SearchInsertPositionTest
36	Valid Sudoku	Medium	ValidSudokuTest
37	Sudoku Solver	Hard	SudokuSolverTest
38	Count and Say	Medium	CountAndSayTest
39	Combination Sum	Medium	CombinationSumTest
40	Combination Sum II	Medium	CombinationSumIITest
41	First Missing Positive	Hard	FirstMissingPositiveTest
42	Trapping Rain Water	Hard	TrappingRainWaterTest
43	Multiply Strings	Medium	MultiplyStringsTest
44	Wildcard Matching	Hard	WildcardMatchingTest
45	Jump Game II	Medium	JumpGameIITest	✅
46	Permutations	Medium	PermutationsTest
47	Permutations II	Medium	PermutationsIITest
48	Rotate Image	Medium	RotateImageTest
49	Group Anagrams	Medium	GroupAnagramsTest	✅
50	Pow(x, n)	Medium	PowXNTest
51	N-Queens	Hard	NQueensTest
52	N-Queens II	Hard	NQueensIITest
53	Maximum Subarray	Medium	MaximumSubarrayTest	✅
54	Spiral Matrix	Medium	SpiralMatrixTest	✅
55	Jump Game	Medium	JumpGameTest	✅
56	Merge Intervals	Medium	MergeIntervalsTest	✅
57	Insert Interval	Medium	InsertIntervalTest
58	Length of Last Word	Easy	LengthOfLastWordTest
59	Spiral Matrix II	Medium	SpiralMatrixIITest
60	Permutation Sequence	Hard	PermutationSequenceTest
61	Rotate List	Medium	RotateListTest
62	Unique Paths	Medium	UniquePathsTest
63	Unique Paths II	Medium	UniquePathsIITest
64	Minimum Path Sum	Medium	MinimumPathSumTest
65	Valid Number	Hard	ValidNumberTest
66	Plus One	Easy	PlusOneTest
67	Add Binary	Easy	AddBinaryTest	✅
68	Text Justification	Hard	TextJustificationTest
69	Sqrt(x)	Easy	SqrtXTest
70	Climbing Stairs	Easy	ClimbingStairsTest
71	Simplify Path	Medium	SimplifyPathTest
72	Edit Distance	Medium	EditDistanceTest
73	Set Matrix Zeroes	Medium	SetMatrixZeroesTest
74	Search a 2D Matrix	Medium	SearchA2DMatrixTest
75	Sort Colors	Medium	SortColorsTest
76	Minimum Window Substring	Hard	MinimumWindowSubstringTest
77	Combinations	Medium	CombinationsTest
78	Subsets	Medium	SubsetsTest	✅
79	Word Search	Medium	WordSearchTest
80	Remove Duplicates from Sorted Array II	Medium	RemoveDuplicatesFromSortedArrayIITest	✅
81	Search in Rotated Sorted Array II	Medium	SearchInRotatedSortedArrayIITest
82	Remove Duplicates from Sorted List II	Medium	RemoveDuplicatesFromSortedListIITest
83	Remove Duplicates from Sorted List	Easy	RemoveDuplicatesFromSortedListTest
84	Largest Rectangle in Histogram	Hard	LargestRectangleInHistogramTest	✅
85	Maximal Rectangle	Hard	MaximalRectangleTest	✅
86	Partition List	Medium	PartitionListTest
87	Scramble String	Hard	ScrambleStringTest
88	Merge Sorted Array	Easy	MergeSortedArrayTest	✅
89	Gray Code	Medium	GrayCodeTest
90	Subsets II	Medium	SubsetsIITest
91	Decode Ways	Medium	DecodeWaysTest
92	Reverse Linked List II	Medium	ReverseLinkedListIITest
93	Restore IP Addresses	Medium	RestoreIPAddressesTest
94	Binary Tree Inorder Traversal	Easy	BinaryTreeInorderTraversalTest	✅
95	Unique Binary Search Trees II	Medium	UniqueBinarySearchTreesIITest
96	Unique Binary Search Trees	Medium	UniqueBinarySearchTreesTest
97	Interleaving String	Medium	InterleavingStringTest
98	Validate Binary Search Tree	Medium	ValidateBinarySearchTreeTest
99	Recover Binary Search Tree	Medium	RecoverBinarySearchTreeTest
100	Same Tree	Easy	SameTreeTest
101	Symmetric Tree	Easy	SymmetricTreeTest
102	Binary Tree Level Order Traversal	Medium	BinaryTreeLevelOrderTraversalTest
103	Binary Tree Zigzag Level Order Traversal	Medium	BinaryTreeZigzagLevelOrderTraversalTest	✅
104	Maximum Depth of Binary Tree	Easy	MaximumDepthOfBinaryTreeTest	✅
105	Construct Binary Tree from Preorder and Inorder Traversal	Medium	ConstructBinaryTreeFromPreorderAndInorderTraversalTest	✅
106	Construct Binary Tree from Inorder and Postorder Traversal	Medium	ConstructBinaryTreeFromInorderAndPostorderTraversalTest
107	Binary Tree Level Order Traversal II	Medium	BinaryTreeLevelOrderTraversalIITest
108	Convert Sorted Array to Binary Search Tree	Easy	ConvertSortedArrayToBinarySearchTreeTest
109	Convert Sorted List to Binary Search Tree	Medium	ConvertSortedListToBinarySearchTreeTest
110	Balanced Binary Tree	Easy	BalancedBinaryTreeTest
111	Minimum Depth of Binary Tree	Easy	MinimumDepthOfBinaryTreeTest
112	Path Sum	Easy	PathSumTest
113	Path Sum II	Medium	PathSumIITest
114	Flatten Binary Tree to Linked List	Medium	FlattenBinaryTreeToLinkedListTest
115	Distinct Subsequences	Hard	DistinctSubsequencesTest
116	Populating Next Right Pointers in Each Node	Medium	PopulatingNextRightPointersInEachNodeTest
117	Populating Next Right Pointers in Each Node II	Medium	PopulatingNextRightPointersInEachNodeIITest
118	Pascal's Triangle	Easy	PascalsTriangleTest	✅
119	Pascal's Triangle II	Easy	PascalsTriangleIITest
120	Triangle	Medium	TriangleTest
121	Best Time to Buy and Sell Stock	Easy	BestTimeToBuyAndSellStockTest
122	Best Time to Buy and Sell Stock II	Medium	BestTimeToBuyAndSellStockIITest	✅
123	Best Time to Buy and Sell Stock III	Hard	BestTimeToBuyAndSellStockIIITest
124	Binary Tree Maximum Path Sum	Hard	BinaryTreeMaximumPathSumTest
125	Valid Palindrome	Easy	ValidPalindromeTest
126	Word Ladder II	Hard	WordLadderIITest
127	Word Ladder	Hard	WordLadderTest
128	Longest Consecutive Sequence	Medium	LongestConsecutiveSequenceTest
129	Sum Root to Leaf Numbers	Medium	SumRootToLeafNumbersTest
130	Surrounded Regions	Medium	SurroundedRegionsTest
131	Palindrome Partitioning	Medium	PalindromePartitioningTest
132	Palindrome Partitioning II	Hard	PalindromePartitioningIITest
133	Clone Graph	Medium	CloneGraphTest
134	Gas Station	Medium	GasStationTest
135	Candy	Hard	CandyTest
136	Single Number	Easy	SingleNumberTest	✅
137	Single Number II	Medium	SingleNumberIITest
138	Copy List with Random Pointer	Medium	CopyListWithRandomPointerTest
139	Word Break	Medium	WordBreakTest
140	Word Break II	Hard	WordBreakIITest
141	Linked List Cycle	Easy	LinkedListCycleTest
142	Linked List Cycle II	Medium	LinkedListCycleIITest
143	Reorder List	Medium	ReorderListTest
144	Binary Tree Preorder Traversal	Easy	BinaryTreePreorderTraversalTest
145	Binary Tree Postorder Traversal	Easy	BinaryTreePostorderTraversalTest
146	LRU Cache	Medium	LRUCacheTest	✅
147	Insertion Sort List	Medium	InsertionSortListTest
148	Sort List	Medium	SortListTest
149	Max Points on a Line	Hard	MaxPointsOnALineTest
150	Evaluate Reverse Polish Notation	Medium	EvaluateReversePolishNotationTest
151	Reverse Words in a String	Medium	ReverseWordsInAStringTest
152	Maximum Product Subarray	Medium	MaximumProductSubarrayTest
153	Find Minimum in Rotated Sorted Array	Medium	FindMinimumInRotatedSortedArrayTest
154	Find Minimum in Rotated Sorted Array II	Hard	FindMinimumInRotatedSortedArrayIITest
155	Min Stack	Medium	MinStackTest	✅
160	Intersection of Two Linked Lists	Easy	IntersectionOfTwoLinkedListsTest
162	Find Peak Element	Medium	FindPeakElementTest
164	Maximum Gap	Medium	MaximumGapTest
165	Compare Version Numbers	Medium	CompareVersionNumbersTest
166	Fraction to Recurring Decimal	Medium	FractionToRecurringDecimalTest
167	Two Sum II - Input Array Is Sorted	Medium	TwoSumIIInputArrayIsSortedTest
168	Excel Sheet Column Title	Easy	ExcelSheetColumnTitleTest	✅
169	Majority Element	Easy	MajorityElementTest	✅
171	Excel Sheet Column Number	Easy	ExcelSheetColumnNumberTest	✅
172	Factorial Trailing Zeroes	Medium	FactorialTrailingZeroesTest	✅
173	Binary Search Tree Iterator	Medium	BinarySearchTreeIteratorTest
174	Dungeon Game	Hard	DungeonGameTest
179	Largest Number	Medium	LargestNumberTest
187	Repeated DNA Sequences	Medium	RepeatedDNASequencesTest
188	Best Time to Buy and Sell Stock IV	Hard	BestTimeToBuyAndSellStockIVTest
189	Rotate Array	Medium	RotateArrayTest	✅
190	Reverse Bits	Easy	ReverseBitsTest
191	Number of 1 Bits	Easy	NumberOf1BitsTest
198	House Robber	Medium	HouseRobberTest	✅
199	Binary Tree Right Side View	Medium	BinaryTreeRightSideViewTest
200	Number of Islands	Medium	NumberOfIslandsTest	✅
202	Happy Number	Easy	HappyNumberTest	✅
213	House Robber II	Medium	HouseRobberIITest	✅
221	Maximal Square	Medium	MaximalSquareTest	✅
238	Product of Array Except Self	Medium	ProductOfArrayExceptSelfTest	✅
242	Valid Anagram	Easy	ValidAnagramTest	✅
283	Move Zeroes	Easy	MoveZeroesTest	✅
295	Find Median from Data Stream	Hard	FindMedianFromDataStreamTest	✅
297	Serialize and Deserialize Binary Tree	Hard	SerializeAndDeserializeBinaryTreeTest	✅
337	House Robber III	Medium	HouseRobberIIITest	✅
338	Counting Bits	Easy	CountingBitsTest	✅
344	Reverse String	Easy	ReverseStringTest	✅
371	Sum of Two Integers	Medium	SumOfTwoIntegersTest	✅
412	Fizz Buzz	Easy	FizzBuzzTest	✅
448	Find All Numbers Disappeared in an Array	Easy	FindAllNumbersDisappearedInAnArrayTest	✅
461	Hamming Distance	Easy	HammingDistanceTest	✅
485	Max Consecutive Ones	Easy	MaxConsecutiveOnesTest	✅
496	Next Greater Element I	Easy	NextGreaterElementITest	✅
509	Fibonacci Number	Easy	FibonacciNumberTest	✅
525	Contiguous Array	Medium	ContiguousArrayTest	✅
543	Diameter of Binary Tree	Easy	DiameterOfBinaryTreeTest	✅
561	Array Partition	Easy	ArrayPartitionTest	✅
617	Merge Two Binary Trees	Easy	MergeTwoBinaryTreesTest	✅
645	Set Mismatch	Easy	SetMismatchTest	✅
657	Robot Return to Origin	Easy	RobotReturnToOriginTest	✅
718	Maximum Length of Repeated Subarray	Medium	MaximumLengthOfRepeatedSubarrayTest	✅
728	Self Dividing Numbers	Easy	SelfDividingNumbersTest	✅
740	Delete and Earn	Medium	DeleteAndEarnTest	✅
760	Find Anagram Mappings	Easy	FindAnagramMappingsTest	✅
766	Toeplitz Matrix	Easy	ToeplitzMatrixTest	✅
844	Backspace String Compare	Easy	BackspaceStringCompareTest	✅
876	Middle of the Linked List	Easy	MiddleOfTheLinkedListTest	✅
1025	Divisor Game	Easy	DivisorGameTest	✅
1028	Recover a Tree From Preorder Traversal	Hard	RecoverFromPreorderTest
1046	Last Stone Weight	Easy	LastStoneWeightTest	✅
1114	Print in Order	Easy	PrintInOrderTest	✅
1115	Print FooBar Alternately	Medium	PrintFooBarAlternatelyTest	✅
1137	N-th Tribonacci Number	Easy	NThTribonacciNumberTest	✅
1189	Maximum Number of Balloons	Easy	MaximumNumberOfBalloonsTest	✅
1365	How Many Numbers Are Smaller Than the Current Number	Easy	HowManyNumbersAreSmallerThanTheCurrentNumberTest	✅
1426	Counting Elements	Easy	CountingElementsTest	✅
1470	Shuffle the Array	Easy	ShuffleTheArrayTest	✅
1475	Final Prices With a Special Discount in a Shop	Easy	FinalPricesWithASpecialDiscountInAShopTest	✅
1861	Rotating the Box	Medium	RotatingTheBoxTest	✅
1929	Concatenation of Array	Easy	ConcatenationOfArrayTest	✅
3863	Minimum Operations to Sort a String	Medium	MinimumOperationsToSortAStringTest	✅