LeetCode

Resources

1. AlgoMonster - Questions/subjetcs patterns in coding interviews.
   • Includes specific data for Amazon, Apple, Google, Meta.
   • Includes ROI for different subjects in terms of time investments.
   • Flow chart of how to approach a problem.
   • Honestly, a lot more.
2. InterviewBit - Similar to LeetCode.
   • Shows company questions for free.
   • Has a focus on timing solutions.
3. NeetCode.io, NeetCode YouTube channel.
   • Subjects roadmap for learning and practicing.
   • NeetCode 75 & NeetCode 150 for interview preparations.
   • Videos of detailed solutions with explanations - both intuitively and programmatically.
   • Strategy of learning and solving LeetCode questions.
4. Codility - Great for simulating real exams.
   • Lessons.
   • Simulates a real exam by:
     • Focus on writing your own testcases. No testcases are provided by this website.
     • Timed exam.
     • Once you submit your solution:
       • You receive a grade.
       • You see an explanation of successes/failures. Testcases are divided to categories such as edge cases, time complexity, etc., but no explicit testcases are provided/shown.
       • You need to restart the exam to submit a new solution.

Solutions

LeetCode profile

Solutions to the LeetCode problems I solved/studied so far:

#	Title	Solution	Difficulty	Notes
3	Longest Substring Without Repearing Characters	Python3	Medium	Sliding Window
13	Roman to Integer	Python3	Easy
20	Valid Parentheses	Java	Easy
40	Combination Sum II	Python3	Medium
41	First Missing Positive	C	Hard
42	Trapping Rain Water	Python3	Hard	Solution using arrays Solution using two pointers
50	Pow(x, n)	Python3	Medium
56	Merge Intervals	Python3	Medium
69	Sqrt(x)	Java	Easy
70	Climbing Stairs	Python3	Easy
75	Sort Colors	Python3	Medium	Counting Sort (two-pass), Two pointers (one-pass)
78	Subsets	Python3	Medium
94	Binary Tree Inorder Traversal	Java	Easy
118	Pascal's Triangle	Python3	Easy
119	Pascal's Triangle II	Python3	Easy
121	Best Time to Buy and Sell Stock	Python3	Easy
131	Palindrome Partitioning	Python3	Medium
136	Single Number	C	Easy
137	Single Number II	C	Medium
140	Word Break II	Python3	Hard
141	Linked List Cycle	Java	Easy
145	Binary Tree Postorder Traversal	Python3	Easy
146	LRU Cache	Python3	Medium	Ordered Dictionary, Doubly Linked List & Hashmap
165	Compare Version Numbers	Python3	Medium
179	Largest Number	Python3	Medium
200	Number of Islands	Python3	Medium	BFS on a matrix
206	Reverse Linked List	C	Easy
214	Shortest Palindrome	Python3	Hard	Rabin–Karp algorithm
215	Kth Largest Element in an Array	Python3	Medium	One liner
237	Delete Node in a Linked List	Python3	Medium
241	Different Ways to Add Parentheses	Python3	Medium
260	Single Number III	C	Medium
264	Ugly Number II	Python3	Medium	Mathematical properties
273	Integer to English Words	Python3	Hard
287	Find the Duplicate Number	C	Medium	Floyd's cycle detection
330	Patching Array	Python3	Hard	Mathematical properties
338	Counting Bits	C	Easy
344	Reverse String	C	Easy
350	Intersection of Two Arrays II	Python3	Easy
386	Lexicographical Numbers	Python3	Medium
409	Longest Palindrome	Python3	Easy
432	All O`one Data Structure	Python3	Medium
440	K-th Smallest in Lexicographical Order	Python3	Hard
476	Number Complement	Python3	Easy
502	IPO	Python3	Hard
506	Relative Ranks	Python3	Easy
523	Continuous Subarray Sum	Java	Medium	Mathematical properties
539	Minimum Time Difference	Python3	Medium
552	Student Attendance Record II	Java	Hard
564	Find the Closest Palindrome	Python3	Hard
567	Permutation in String	Java	Medium
590	N-ary Tree Postorver Traversal	Python3	Easy
592	Fraction Addition and Subtraction	Python3	Medium
624	Maximum Distance in Arrays	Python3	Medium
632	Smallest Range Covering Elements from K Lists	Python3	Hard
633	Sum of Square Numbers	Python3	Medium	Mathematical properties
641	Design Circular Deque	Python3	Medium
648	Replace Words	Python3	Medium
650	2 Keys Keyboard	Python3	Medium	Dynamic Programming
664	Strange Printer	Python3	Hard	Dynamic Programming
670	Maximum Swap	Python3	Medium
703	Kth Largest Element in a Stream	Python3	Easy
719	Find K-th Smallest Pair Distance	Python3	Hard	Sliding Window & Binary Search on the result
725	Split Linked List in Parts	Python3	Medium
726	Number of Atoms	Python3	Hard	Parsing string
729	My Calendar I	Python3	Medium
731	My Calendar II	Python3	Medium
771	Jewels and Stones	Python3	Easy
773	Sliding Puzzle	Python3	Hard
786	K-th Smallest Prime Fraction	C	Medium
796	Rotate String	Java	Easy
826	Most Profit Assigning Work	Python3	Medium
840	Magic Squares In Grid	Python3	Medium
846	Hand of Straights	Python3	Medium
857	Minimum Cost to Hire K Workers	Python3	Hard
860	Lemonade Change	Python3	Easy
861	Score After Flipping Matrix	Python3	Medium
862	Shortest Subarray with Sum at Least K	Python3	Hard
874	Walking Robot Simulation	Python3	Medium
881	Boats to Save People	Python3	Medium
884	Uncommon Words from Two Sentences	Python3	Easy
885	Spiral Matrix III	Python3	Medium
912	Sort an Array	Python3	Medium	Implement sorting algorithm without built-in functions. Merge Sort, Heap Sort, Counting Sort
921	Minimum Add to Make Parentheses Valid	Python3	Medium
938	Range Sum of BST	C	Easy
945	Minimum Increment to Make Array Unique	Python3	Medium
947	Most Stones Removed with Same Row or Column	Python3	Medium	Union Find
951	Flip Equivalent Binary Trees	Python3	Medium
959	Regions Cut By Slashes	Python3	Medium	Question can be mapped to Number of Islands (#200)
962	Maximum Width Ramp	Python3	Medium
973	K Closest Points to Origin	Python3	Medium	Heap / sort by lambda function
974	Subarray Sum Divisible by K	Java, Python3	Medium
979	Distribute Coins in Binary Tree	C	Medium	DFS
995	Minimum Number of K Consecutive Bit Flips	Python3	Hard	Sliding Window & Bit Manipulation Great editorial
1002	Find Common Characters	Java	Easy
1038	Binary Search Tree to Greater Sum Tree	Python3	Medium	BST, DFS
1051	Height Checker	Java, Python3	Easy	Counting Sort
1052	Grumpy Bookstore Owner	Python3	Medium	Sliding Window
1072	Flip Columns for Maximum Number of Equal Rows	Python3	Medium
1105	Filling Bookcase Shelves	Python3	Medium	Dynamic Programming
1106	Parsing A Boolean Expression	Python3	Hard
1110	Delete Nodes and Return Forest	Python3	Medium
1122	Relative Sort Array	Python3	Easy
1140	Stone Game II	Python3	Medium	Dynamic Programming
1190	Reverse Substrings Between Each Pair of Parentheses	Python3	Medium
1208	Get Equal Substrings Within Budget	C	Medium	Sliding Window
1219	Path with Maximum Gold	Java	Medium	DFS & Backtracking
1233	Remove Sub-Folders from the Filesystem	Python3	Medium
1248	Count Number of Nice Subarrays	Python3	Medium	Sliding Window
1255	Maximum Score Words Formed by Letters	C	Hard
1268	Search Suggestions System	Python3	Medium
1277	Count Square Submatrices with All Ones	Python3	Medium
1310	XOR Queries of a Subarray	Python3	Medium
1325	Delete Leaves With a Given Value	C	Medium	DFS
1331	Rank Transform of an Array	Java	Easy
1334	Find the City With the Smallest Number of Neighbors at a Threshold Distance	Python3	Medium	Shortest Path from every node to every node. Dijkstra's algorithm, Floyd-Warshall algorithm
1342	Number of Steps to Reduce a Number to Zero	Python3	Easy
1367	Linked List in Binary Tree	Python3	Medium
1371	Find the Longest Substring Containing Vowels in Even Counts	Python3	Medium
1380	Lucky Numbers in a Matrix	Python3	Easy
1381	Design a Stack With Increment Operation	Python3, Java	Medium
1382	Balance a Binary Search Tree	Python3	Medium
1395	Count Number of Teams	Python3	Medium
1404	Number of Steps to Reduce a Number in Binary Representation to One	C	Medium
1405	Longest Happy String	Python3	Medium
1438	Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit	Python3	Medium	Sliding Window with 2 Heaps
1442	Count Triplets That Can Form Two Arrays of Equal XOR	C	Medium
1460	Make Two Arrays Equal by Reversing Subarrays	Python3	Easy
1480	Running Sum of 1d Array	Java	Easy
1482	Minimum Number of Days to Make m Bouquets	Python3	Medium
1486	XOR Operation in an Array	Python3	Easy
1497	Check If Array Pairs Are Divisible by K	Java	Medium
1508	Range Sum of Sorted Subarray Sums	Python3	Medium
1509	Minimum Difference Between Largest and Smallest Value in Three Moves	Python3	Medium
1512	Number of Good Pairs	Go	Easy
1514	Path with Maximum Probability	Python3	Medium	Maximizing probability instead of minimizing distance. Dijkstra's algorithm, Bellman-Ford algorithm
1518	Water Bottles	Python3	Easy	Mathematical properties
1530	Number of Good Leaf Nodes Pairs	Python3	Medium	DFS, Shortest Path between nodes
1545	Find Kth Bit in Nth Binary String	Python3	Medium
1550	Three Consecutive Odds	Python3	Easy
1552	Magnetic Force Between Two Balls	Python3	Medium	Binary Search
1568	Minimum Number of Days to Disconnect Island	Python3	Hard
1574	Shortest Subarray to be Removed to Make Array Sorted	Python3	Medium
1579	Remove Max Number of Edges to Keep Graph Fully Traversable	Python3	Hard	Union Find, Graph
1590	Make Sum Divisible by P	Java	Medium
1593	Split a String Into the Max Number of Unique Substrings	Python3	Medium
1598	Crawler Log Folder	Python3	Easy
1605	Find Valid Matrix Given Row and Column Sums	Python3	Medium
1608	Special Array With X Elements Greater Than or Equal X	Python3, C	Easy	Python3: Sorting C: Suffix Sum
1636	Sort Array by Increasing Frequency	Python3	Easy
1641	Count Sorted Vowel Strings	Python3	Medium	Dynamic Programming
1652	Defuse the Bomb	Python3	Easy
1653	Minimum Deletions to Make String Balanced	Python3	Medium
1671	Minimum Number of Removals to Make Mountain Array	Python3	Hard
1684	Count the Number of Consistent Strings	Python3, Java	Easy
1689	Partitioning Into Minimum Number of Deci-Binary Numbers	Java	Medium
1701	Average Waiting Time	Python3	Medium
1717	Maximum Score From Removing Substrings	Python3	Medium
1720	Decode XORed Array	Python3	Easy
1752	Check if Array Is Sorted and Rotated	Python3	Easy
1791	Find Center of Star Graph	Python3	Easy
1813	Sentence Similarity III	Python3	Medium
1823	Find the Winner of the Circular Game	Python3	Medium	Mathematical properties
1829	Maximum XOR for Each Query	Java	Medium
1861	Rotating the Box	Python3	Medium
1863	Sum of All Subset XOR Totals	Java, C	Easy	Java: trivial, inefficient C: Black magic AKA bit manipulation
1894	Find the Student that Will Replace the Chalk	Python3	Medium
1905	Count Sub Islands	Python3	Medium
1937	Maximum Number of Points with Cost	Python3	Medium	Dynamic Programming
1942	The Number of the Smallest Unoccupied Chair	Python3	Medium	Two heaps
1945	Sum of Digits of String After Convert	Python3	Easy
1957	Delete Characters to Make Fancy String	Python3	Easy
1963	Minimum Number of Swaps to Make the String Balanced	Python3	Medium
1975	Maximum Matrix Sum	Python3	Medium
2000	Reverse Prefix of Word	C	Easy
2022	Convert 1D Array Into 2D Array	Python3	Easy
2028	Find Missing Observations	Python3	Medium	Mathematical properties
2037	Minimum Number of Moves to Seat Everyone	Python3	Easy
2044	Count Number of Maximum Bitwise-OR Subsets	Python3	Medium
2045	Second Minimum Time to Reach Destination	Python3	Hard	BFS with extra conditions
2053	Kth Distinct String in an Array	Python3	Easy
2058	Find the Minimum and Maximum Number of Nodes Between Critical Points	Python3	Medium
2064	Minimized Maximum of Products Distributed to Any Store	Python3	Medium
2070	Most Beautiful Item for Each Query	Python3	Medium
2096	Step-By-Step Direction From a Binary Tree Node to Another	Python3	Medium	BFS
2134	Minimum Swaps to Group All 1's Together II	Python3	Medium
2181	Merge Nodes in Between Zeros	Python3	Medium
2191	Sort the Jumbled Numbers	Python3	Medium
2192	All Ancestors of a Node in a Directed Acyclic Graph	Python3	Medium
2196	Create Binary Tree From Descriptions	Python3	Medium
2220	Minimum Bit Flips to Convert Number	Python3, Java	Easy
2248	Intersection of Multiple Arrays	Python3	Easy
2257	Count Unguarded Cells in the Grid	Python3	Medium
2275	Largest Combination With Bitwise AND Greater Than Zero	Java	Medium
2285	Maximum Total Importance of Roads	Python3	Medium	Undirected Graph, Greedy
2326	Spiral Matrix IV	Python3	Medium
2331	Evaluate Boolean Binary Tree	C	Easy
2373	Largest Local Value in a Matrix	Java	Easy
2392	Build a Matrix With Conditions	Python3	Hard	Topological Sort, DFS
2406	Divide Intervals Into Minimum Number of Groups	Python3	Medium
2416	Sum of Prefix Scores of Strings	Python3	Hard	Trie / Prefix Tree
2418	Sort the People	Python3	Easy
2419	Longest Subarray With Maximum Bitwise AND	Python3	Medium
2441	Largest Positive Integer That Exists With Its Negative	Python3	Easy
2458	Height of Binary Tree After Subtree Removal Queries	Python3	Hard
2461	Maximum Sum of Distinct Subarrays With Length K	Python3	Medium
2463	Minimum Total Distance Traveled	Python3	Hard
2469	Convert the Temperature	Go	Easy
2486	Append Characters to String to Make Subsequence	C	Medium
2487	Remove Nodes From Linked List	Java	Medium	Monotonic Stack
2490	Circular Sentence	Python3	Easy
2491	Divide Players Into Teams of Equal Skill	Java	Medium
2501	Longest Square Streak in an Array	Python3	Medium
2516	Take K of Each Character From Left and Right	Python3	Medium
2530	Maximal Score After Applying K Operations	Python3	Medium
2563	Count the Number of Fair Pairs	Python3	Medium
2574	Left and Right Sum Differences	Java	Easy
2582	Pass the Pillow	Python3	Easy	Mathematical properties
2583	Kth Largest Sum in a Binary Tree	Python3	Medium
2597	The Number of Beautiful Subsets	Python3	Medium	Backtracking
2601	Prime Subtraction Operation	Python3	Medium
2641	Cousins in Binary Tree II	Python3	Medium
2657	Find the Prefix Common Array of Two Arrays	Java	Medium
2678	Number of Senior Citizens	Python3	Easy
2684	Maximum Number of Moves in a Grid	Python3, Java	Medium
2696	Minimum String Length After Removing Substrings	Python3	Easy
2699	Modify Graph Edge Weights	Python3	Hard	Dijkstra's algorithm
2707	Extra Characters in a String	Python3	Medium	Trie / Prefix Tree
2751	Robot Collisions	Python3	Hard
2807	Insert Greatest Common Divisors in Linked List	Python3	Medium
2812	Find the Safest Path in a Grid	Java	Medium	Multi-source BFS
2816	Double a Number Represented as a Linked List	C	Medium
2859	Sum of Values at Indices With K Set Bits	Python3	Easy
2886	Change Data Type	Python3	Easy
2914	Minimum Number of Changes to Make Binary String Beautiful	Python3	Medium
2924	Find Champion II	Python3	Medium
2938	Separate Black and White Balls	Python3	Medium
2952	Minimum Number of Coins to be Added	Python3	Medium	Mathematical properties
2976	Minimum Cost to Convert String I	Python3	Medium	Dijkstra's algorithm, Floyd-Warshall algorithm
3011	Find if Array Can Be Sorted	Java	Medium
3016	Minimum Number of Pushes to Type Word II	Python3	Medium
3043	Find the Length of the Longest Common Prefix	Python3	Medium
3068	Find the Maximum Sum of Node Values	C	Hard
3075	Maximize Happiness of Selected Children	Java, Python3	Medium	Java: Max Heap Python3: Sorting
3097	Shortest Subarray With OR at Least K II	Python3	Medium
3110	Score of a String	Java	Easy
3133	Minimum Array End	Java	Medium
3163	String Compression III	Python3	Medium
3217	Delete Nodes From Linked List Present in Array	Python3	Medium
3254	Find the Power of K-Size Subarrays I	Python3	Medium