Leetcode Top Interview 🎯

This repository contains solutions to the Leetcode Top Interview 150 problems.

These problems are commonly asked in technical interviews and cover a wide range of topics, including data structures, algorithms, and problem-solving techniques.

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Table of Contents 📖

• What is Leetcode? 🧑‍💻
• About the Top Interview 150 Collection Questions 🏆
• Tips for Solving Problems 💡
• Repository Structure 🗂️
• How to Use This Repository 🚀
• Resources 📚

What is Leetcode? 🧑‍💻

Leetcode is a popular online platform that provides a collection of coding challenges. Software engineers and interview candidates widely use it to practice coding skills and prepare for technical interviews. Leetcode offers many problems to solve, classified by difficulty level and topic.

About the Top Interview 150 Collection 🏆

The Top Interview 150 collection on Leetcode is a curated set of 150 interview questions that top tech companies frequently ask. These questions are carefully selected to cover essential concepts and algorithms that interviewers expect candidates to be familiar with.

Id	Problem	Difficulty	Signal	Status
Array / String
1	Merge Sorted Array	Easy	🟢	✅
2	Remove Element	Easy	🟢	✅
3	Remove Duplicates from Sorted Array	Easy	🟢	✅
4	Remove Duplicates from Sorted Array II	Medium	🟡	✅
5	Majority Element	Easy	🟢	✅
6	Rotate Array	Medium	🟡	✅
7	Best Time to Buy and Sell Stock	Easy	🟢	✅
8	Best Time to Buy and Sell Stock II	Medium	🟡	✅
9	Jump Game	Medium	🟡	✅
10	Jump Game II	Medium	🟡	✅
11	H-Index	Medium	🟡	✅
12	Insert Delete GetRandom O(1)	Medium	🟡	✅
13	Product of Array Except Self	Medium	🟡	✅
14	Gas Station	Medium	🟡	✅
15	Candy	Hard	🔴	✅
16	Trapping Rain Water	Hard	🔴	✅
17	Roman to Integer	Easy	🟢	✅
18	Integer to Roman	Medium	🟡	✅
19	Length of Last Word	Easy	🟢	✅
20	Longest Common Prefix	Easy	🟢	✅
21	Reverse Words in a String	Medium	🟡	✅
22	Zigzag Conversion	Medium	🟡	✅
23	Find the Index of the First Occurrence in a String	Easy	🟢	✅
24	Text Justification	Hard	🔴	✅
Two Pointers
25	Valid Palindrome	Easy	🟢	✅
26	Is Subsequence	Easy	🟢	✅
27	Two Sum II - Input Array Is Sorted	Medium	🟡	✅
28	Container With Most Water	Medium	🟡	✅
29	3Sum	Medium	🟡	✅
Sliding Window
30	Minimum Size Subarray Sum	Medium	🟡	✅
31	Longest Substring Without Repeating Characters	Medium	🟡	✅
32	Substring with Concatenation of All Words	Hard	🔴	✅
33	Minimum Window Substring	Hard	🔴	✅
Matrix
34	Valid Sudoku	Medium	🟡	✅
35	Spiral Matrix	Medium	🟡	✅
36	Rotate Image	Medium	🟡	✅
37	Set Matrix Zeroes	Medium	🟡	✅
38	Game of Life	Medium	🟡	✅
Hashmap
39	Ransom Note	Easy	🟢	✅
40	Isomorphic Strings	Easy	🟢	✅
41	Word Pattern	Easy	🟢	✅
42	Valid Anagram	Easy	🟢	✅
43	Group Anagrams	Medium	🟡	✅
44	Two Sum	Easy	🟢	✅
45	Happy Number	Easy	🟢	✅
46	Contains Duplicate II	Easy	🟢	✅
47	Longest Consecutive Sequence	Medium	🟡	✅
Intervals
48	Summary Ranges	Easy	🟢	✅
49	Merge Intervals	Medium	🟡	✅
50	Insert Interval	Medium	🟡	✅
51	Minimum Number of Arrows to Burst Balloons	Medium	🟡	✅
Stack
52	Valid Parentheses	Easy	🟢	✅
53	Simplify Path	Medium	🟡	✅
54	Min Stack	Medium	🟡	✅
55	Evaluate Reverse Polish Notation	Medium	🟡	✅
56	Basic Calculator	Hard	🔴	✅
Linked List
57	Linked List Cycle	Easy	🟢	✅
58	Add Two Numbers	Medium	🟡	✅
59	Merge Two Sorted Lists	Easy	🟢	✅
60	Copy List with Random Pointer	Medium	🟡	✅
61	Reverse Linked List II	Medium	🟡	✅
62	Reverse Nodes in k-Group	Hard	🔴	✅
63	Remove Nth Node From End of List	Medium	🟡	✅
64	Remove Duplicates from Sorted List II	Medium	🟡	✅
65	Rotate List	Medium	🟡	✅
66	Partition List	Medium	🟡	✅
67	LRU Cache	Medium	🟡	✅
Binary Tree General
68	Maximum Depth of Binary Tree	Easy	🟢	✅
69	Same Tree	Easy	🟢	✅
70	Invert Binary Tree	Easy	🟢	✅
71	Symmetric Tree	Easy	🟢	✅
72	Construct Binary Tree from Preorder and Inorder Traversal	Medium	🟡	✅
73	Construct Binary Tree from Inorder and Postorder Traversal	Medium	🟡	✅
74	Populating Next Right Pointers in Each Node II	Medium	🟡	✅
75	Flatten Binary Tree to Linked List	Medium	🟡
76	Path Sum	Easy	🟢
77	Sum Root to Leaf Numbers	Medium	🟡
78	Binary Tree Maximum Path Sum	Hard	🔴
79	Binary Search Tree Iterator	Medium	🟡
80	Count Complete Tree Nodes	Easy	🟢
81	Lowest Common Ancestor of a Binary Tree	Medium	🟡
Binary Tree BFS
8282	Binary Tree Right Side View	Medium	🟡
83	Average of Levels in Binary Tree	Easy	🟢
84	Binary Tree Level Order Traversal	Medium	🟡
85	Binary Tree Zigzag Level Order Traversal	Medium	🟡
Binary Search Tree
86	Minimum Absolute Difference in BST	Easy	🟢
87	Kth Smallest Element in a BST	Medium	🟡
88	Validate Binary Search Tree	Medium	🟡
Graph General
89	Number of Islands	Medium	🟡
90	Surrounded Regions	Medium	🟡
91	Clone Graph	Medium	🟡
92	Evaluate Division	Medium	🟡
93	Course Schedule	Medium	🟡
94	Course Schedule II	Medium	🟡
Graph BFS
95	Snakes and Ladders	Medium	🟡
96	Minimum Genetic Mutation	Medium	🟡
97	Word Ladder	Hard	🔴
Trie
98	Implement Trie (Prefix Tree)	Medium	🟡
99	Design Add and Search Words Data Structure	Medium	🟡
100	Word Search II	Hard	🔴
Backtracking
101	Letter Combinations of a Phone Number	Medium	🟡
102	Combinations	Medium	🟡
103	Permutations	Medium	🟡
104	Combination Sum	Medium	🟡
105	N-Queens II	Hard	🔴
106	Generate Parentheses	Medium	🟡
107	Word Search	Medium	🟡
Divide & Conquer
108	Convert Sorted Array to Binary Search Tree	Easy	🟢
109	Sort List	Medium	🟡
110	Construct Quad Tree	Medium	🟡
111	Merge k Sorted Lists	Hard	🔴
Kadane's Algorithm
112	Maximum Subarray	Medium	🟡
113	Maximum Sum Circular Subarray	Medium	🟡
Binary Search
114	Search Insert Position	Easy	🟢
115	Search a 2D Matrix	Medium	🟡
116	Find Peak Element	Medium	🟡
117	Search in Rotated Sorted Array	Medium	🟡
118	Find First and Last Position of Element in Sorted Array	Medium	🟡
119	Find Minimum in Rotated Sorted Array	Medium	🟡
120	Median of Two Sorted Arrays	Hard	🔴
Heap
121	Kth Largest Element in an Array	Medium	🟡
122	IPO	Hard	🔴
123	Find K Pairs with Smallest Sums	Medium	🟡
124	Find Median from Data Stream	Hard	🔴
Bit Manipulation
125	Add Binary	Easy	🟢
126	Reverse Bits	Easy	🟢
127	Number of 1 Bits	Easy	🟢
128	Single Number	Easy	🟢
129	Single Number II	Medium	🟡
130	Bitwise AND of Numbers Range	Medium	🟡
Math
131	Palindrome Number	Easy	🟢
132	Plus One	Easy	🟢
133	Factorial Trailing Zeroes	Medium	🟡
134	Sqrt(x)	Easy	🟢
135	Pow(x, n)	Medium	🟡
136	Max Points on a Line	Hard	🔴
1D DP
137	Climbing Stairs	Easy	🟢
138	House Robber	Medium	🟡
139	Word Break	Medium	🟡
140	Coin Change	Medium	🟡
141	Longest Increasing Subsequence	Medium	🟡
Multidimensional DP
142	Triangle	Medium	🟡
143	Minimum Path Sum	Medium	🟡
144	Unique Paths II	Medium	🟡
145	Longest Palindromic Substring	Medium	🟡
146	Interleaving String	Medium	🟡
147	Edit Distance	Medium	🟡
148	Best Time to Buy and Sell Stock III	Hard	🔴
149	Best Time to Buy and Sell Stock IV	Hard	🔴
150	Maximal Square	Medium	🟡

Tips for Solving Problems 💡

SSome helpful strategies to tackle different types of problems in this repository:

Strategy	Description	Example Use Case
Heap for Top K Elements 🔼	Use a Heap to find the top K largest, smallest, or closest elements among N elements. Efficient for problems requiring constant updates.	Finding the top K largest numbers in a list.
Binary Search or Two Pointers for Sorted Input 🔍➡️⬅️	Use Binary Search or Two Pointers for sorted arrays, lists, or matrices to optimize the solution.	Searching for an element in a sorted array.
Backtracking or BFS for Combinations and Permutations 🔄🔍	Use Backtracking or BFS for problems requiring exploration of all combinations or permutations.	Finding all permutations of a set.
BFS or DFS for Trees and Graphs 🌳🔗	Use BFS or DFS for tree or graph-related problems.	Searching a graph or binary tree.
Stack for Converting Recursion to Iteration 📚	Convert recursion problems into iterative solutions using a stack to simulate the call stack.	Performing a recursive search without using recursion.
Optimizing Array Problems 📊	Optimize array problems from O(n²) to O(n) using a HashMap or Set, or to O(n log n) using sorting.	Finding duplicate elements in an array.
Dynamic Programming for Optimization Problems 🚀	Dynamic Programming is essential for problems that involve maximizing or minimizing values, using results from previous subproblems.	Finding the maximum value in a sequence.
Trie for String Manipulation 🔤	For multiple strings or searching for common substrings, use a Trie or HashMap. A Trie is the most suitable data structure when manipulating multiple strings.	Searching or manipulating multiple strings efficiently.
Fast & Slow Pointers for Linked Lists 🔄🏃‍♂️🏃‍♀️	Use Fast & Slow Pointers to efficiently solve LinkedList problems with restricted memory usage, like detecting cycles or finding the middle element.	Detecting cycles or finding the middle of a linked list.

Repository Structure 🗂️

This repository is organized by problem number, with each problem having its own directory.

Inside each problem directory, you will find the solution file(s) along with a README file that provides a problem description, constraints, and additional notes if necessary.

How to Use This Repository 🚀

Navigate through the problem directories to explore solutions. Each directory contains the solution files, including explanations and sample input/output.

You can practice implementing your solutions and compare them with those provided.

Feel free to contribute by submitting your solutions or improvements. Open a pull request to share your contributions.

I recommend contributions for new languages, as currently, the solution is only available in Java 🐛.

Resources 📚

• Leetcode
• Top 150 Interview Questions - Leetcode
• GitBook Solution

Happy coding and good luck with your interview preparation! 🎉