🎯 Software Engineering Interview Preparation

A comprehensive repository for interview prep: DSA, System Design, SQL, and Machine Coding.

📂 Repository Structure

• solutions/ — LeetCode solutions (JS + Python) organized by difficulty
• SQL/ — SQL interview questions with solutions
• System Design/ — System design case studies for interviews
• Machine Coding/ — Frontend/full-stack machine coding rounds
• DSA/ — DSA cheat sheet, sorting algorithms, patterns
• Design Patterns/ — 12 design patterns with JS/Python/Java code
• DevOps Notes/ — Linux, Docker, CI/CD, Terraform, AWS, Monitoring, Security
• Kubernetes Notes/ — Core concepts, Networking, Storage, Scaling, Helm, GitOps

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🧠 Quick Pattern Recognition Guide

If the problem says...	Think about...
Sorted array	Binary Search, Two Pointers
All permutations/subsets	Backtracking
Tree	DFS, BFS
Graph	DFS, BFS, Union-Find
Linked list	Two Pointers, Fast/Slow
Recursion banned	Stack
In-place	Swap, Store multiple values per pointer
Max/min subarray/subset	Dynamic Programming
Top/least K items	Heap, QuickSelect
Common strings	HashMap, Trie
Optimize space	Bit Manipulation, Greedy
String patterns	Rolling Hash, Sliding Window

Complexity Guide (by constraint n)

n	Target Complexity
n ≤ 12	O(n!)
n ≤ 25	O(2^n)
n ≤ 500	O(n³)
n ≤ 10⁴	O(n²)
n ≤ 10⁶	O(n log n)
n ≤ 10⁸	O(n)
n > 10⁸	O(log n) or O(1)

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LeetCode Top 150 Interview Problems

Array & String (25 problems)

#	Problem	Solution
1	Two Sum	Two Sum
2	Merge Sorted Array	Merge Sorted Array
3	Remove Element	Remove Element
4	Remove Duplicates from Sorted Array	Remove Duplicates
5	Remove Duplicates from Sorted Array II	Remove Duplicates II
6	Majority Element	Majority Element
7	Rotate Array	Rotate Array
8	Best Time to Buy and Sell Stock	Stock I
9	Best Time to Buy and Sell Stock II	Stock II
10	Jump Game	Jump Game
11	Jump Game II	Jump Game II
12	H-Index	H-Index
13	Insert Delete GetRandom O(1)	RandomizedSet
14	Product of Array Except Self	Product Except Self
15	Gas Station	Gas Station
16	Candy	Candy
17	Trapping Rain Water	Trapping Rain Water
18	Roman to Integer	Roman to Integer
19	Integer to Roman	Integer to Roman
20	Length of Last Word	Length of Last Word
21	Longest Common Prefix	Longest Common Prefix
22	Reverse Words in a String	Reverse Words
23	Zigzag Conversion	Zigzag Conversion
24	Find the Index of the First Occurrence in a String	Find First Occurrence
25	Text Justification	Text Justification

Two Pointers (5 problems)

#	Problem	Solution
26	Valid Palindrome	Valid Palindrome
27	Is Subsequence	Is Subsequence
28	Two Sum II - Input Array Is Sorted	Two Sum II
29	Container With Most Water	Container With Most Water
30	3Sum	3sum

Sliding Window (4 problems)

#	Problem	Solution
31	Minimum Size Subarray Sum	Min Subarray Sum
32	Longest Substring Without Repeating Characters	Longest Substring
33	Substring with Concatenation of All Words	Substring Concatenation
34	Minimum Window Substring	Min Window Substring

Matrix (5 problems)

#	Problem	Solution
35	Valid Sudoku	Valid Sudoku
36	Spiral Matrix	Spiral Matrix
37	Rotate Image	Rotate Image
38	Set Matrix Zeroes	Set Matrix Zeroes
39	Game of Life	Game of Life

HashMap (9 problems)

#	Problem	Solution
40	Ransom Note	Ransom Note
41	Isomorphic Strings	Isomorphic Strings
42	Word Pattern	Word Pattern
43	Valid Anagram	Valid Anagram
44	Group Anagrams	Group Anagrams
45	Two Sum	Two Sum
46	Happy Number	Happy Number
47	Contains Duplicate II	Contains Duplicate II
48	Longest Consecutive Sequence	Longest Consecutive

Intervals (4 problems)

#	Problem	Solution
49	Summary Ranges	Summary Ranges
50	Merge Intervals	Merge Intervals
51	Insert Interval	Insert Interval
52	Minimum Number of Arrows to Burst Balloons	Min Arrows

Stack (5 problems)

#	Problem	Solution
53	Valid Parentheses	Valid Parentheses
54	Simplify Path	Simplify Path
55	Min Stack	Min Stack
56	Evaluate Reverse Polish Notation	Evaluate RPN
57	Basic Calculator	Basic Calculator

Linked List (11 problems)

#	Problem	Solution
58	Linked List Cycle	Linked List Cycle
59	Add Two Numbers	Add Two Numbers
60	Merge Two Sorted Lists	Merge Two Sorted Lists
61	Copy List with Random Pointer	Copy List
62	Reverse Linked List II	Reverse Linked List II
63	Reverse Nodes in k-Group	Reverse Nodes in k-Group
64	Remove Nth Node From End of List	Remove Nth
65	Remove Duplicates from Sorted List II	Remove Duplicates Sorted List II
66	Rotate List	Rotate List
67	Partition List	Partition List
68	LRU Cache	LRU Cache

Binary Tree General (14 problems)

#	Problem	Solution
69	Maximum Depth of Binary Tree	Max Depth
70	Same Tree	Same Tree
71	Invert Binary Tree	Invert Binary Tree
72	Symmetric Tree	Symmetric Tree
73	Construct Binary Tree from Preorder and Inorder Traversal	Construct Pre+In
74	Construct Binary Tree from Inorder and Postorder Traversal	Construct In+Post
75	Populating Next Right Pointers in Each Node II	Next Right II
76	Flatten Binary Tree to Linked List	Flatten BT
77	Path Sum	Path Sum
78	Sum Root to Leaf Numbers	Sum Root to Leaf
79	Binary Tree Maximum Path Sum	Max Path Sum
80	Binary Search Tree Iterator	BST Iterator
81	Count Complete Tree Nodes	Count Nodes
82	Lowest Common Ancestor of a Binary Tree	LCA of BT

Binary Tree BFS (4 problems)

#	Problem	Solution
83	Binary Tree Right Side View	Right Side View
84	Average of Levels in Binary Tree	Average of Levels
85	Binary Tree Level Order Traversal	Level Order
86	Binary Tree Zigzag Level Order Traversal	Zigzag Level Order

Binary Search Tree (3 problems)

#	Problem	Solution
87	Minimum Absolute Difference in BST	Min Abs Diff BST
88	Kth Smallest Element in a BST	Kth Smallest BST
89	Validate Binary Search Tree	Validate BST

Graph General (6 problems)

#	Problem	Solution
90	Number of Islands	Number of Islands
91	Surrounded Regions	Surrounded Regions
92	Clone Graph	Clone Graph
93	Evaluate Division	Evaluate Division
94	Course Schedule	Course Schedule
95	Course Schedule II	Course Schedule II

Graph BFS (3 problems)

#	Problem	Solution
96	Snakes and Ladders	Snakes and Ladders
97	Minimum Genetic Mutation	Genetic Mutation
98	Word Ladder	Word Ladder

Trie (3 problems)

#	Problem	Solution
99	Implement Trie (Prefix Tree)	Implement Trie
100	Design Add and Search Words Data Structure	Design Add Search
101	Word Search II	Word Search II

Backtracking (7 problems)

#	Problem	Solution
102	Letter Combinations of a Phone Number	Letter Combinations
103	Combinations	Combinations
104	Permutations	Permutations
105	Combination Sum	Combination Sum
106	N-Queens II	N-Queens II
107	Generate Parentheses	Generate Parentheses
108	Word Search	Word Search

Divide & Conquer (4 problems)

#	Problem	Solution
109	Convert Sorted Array to Binary Search Tree	Convert Sorted Array to BST
110	Sort List	Sort List
111	Construct Quad Tree	Construct Quad Tree
112	Merge k Sorted Lists	Merge k Sorted Lists

Kadane's Algorithm (2 problems)

#	Problem	Solution
113	Maximum Subarray	Maximum Subarray
114	Maximum Sum Circular Subarray	Max Sum Circular

Binary Search (7 problems)

#	Problem	Solution
115	Search Insert Position	Search Insert Position
116	Search a 2D Matrix	Search 2D Matrix
117	Find Peak Element	Find Peak
118	Search in Rotated Sorted Array	Search Rotated
119	Find First and Last Position of Element in Sorted Array	Find First Last
120	Find Minimum in Rotated Sorted Array	Find Min Rotated
121	Median of Two Sorted Arrays	Median of Two Sorted Arrays

Heap (4 problems)

#	Problem	Solution
122	Kth Largest Element in an Array	Kth Largest Element
123	IPO	IPO
124	Find K Pairs with Smallest Sums	Find K Pairs
125	Find Median from Data Stream	Find Median

Bit Manipulation (6 problems)

#	Problem	Solution
126	Add Binary	Add Binary
127	Reverse Bits	Reverse Bits
128	Number of 1 Bits	Number of 1 Bits
129	Single Number	Single Number
130	Single Number II	Single Number II
131	Bitwise AND of Numbers Range	Bitwise AND Range

Math (6 problems)

#	Problem	Solution
132	Palindrome Number	Palindrome Number
133	Plus One	Plus One
134	Factorial Trailing Zeroes	Factorial Trailing Zeroes
135	Sqrt(x)	Sqrt(x)
136	Pow(x, n)	Pow(x, n)
137	Max Points on a Line	Max Points on a Line

1D Dynamic Programming (5 problems)

#	Problem	Solution
138	Climbing Stairs	Climbing Stairs
139	House Robber	House Robber
140	Word Break	Word Break
141	Coin Change	Coin Change
142	Longest Increasing Subsequence	LIS

Multidimensional DP (8 problems)

#	Problem	Solution
143	Triangle	Triangle
144	Minimum Path Sum	Minimum Path Sum
145	Unique Paths II	Unique Paths II
146	Longest Palindromic Substring	Longest Palindromic Substring
147	Interleaving String	Interleaving String
148	Edit Distance	Edit Distance
149	Best Time to Buy and Sell Stock III	Stock III
150	Best Time to Buy and Sell Stock IV	Stock IV

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🔥 Frequently Asked Questions (DE/FAANG Rounds)

➤ Data Engineering Round Problems

#	Problem	Pattern	Solution
1	Top-K Active Users (Last 1 Hour) — Stream	Heap + Sliding Window	JS / Py
2	Order Reconciliation — Two Systems	HashMap + Set Operations	JS / Py
3	Session Grouping + Revenue — 30-min Inactivity	Sorting + Interval Merging	JS / Py

➤ Classic Must-Know Problems

#	Problem	LC	Pattern	Solution
1	LRU Cache + LFU Cache	146 / 460	HashMap + DLL / Freq Map	JS / Py
2	Find Median from Data Stream	295	Two Heaps	JS / Py
3	Word Ladder	127	BFS + Wildcard Preprocessing	JS / Py
4	Merge K Sorted Lists	23	Min-Heap	JS / Py
5	Detect Cycle in Directed Graph	—	DFS 3-color / Kahn's BFS	JS / Py
6	Maximum Subarray Sum (Kadane's)	53	Kadane's / Greedy DP	JS / Py
7	Kth Largest Element in a Stream	703	Min-Heap of Size K	JS / Py
8	Task Scheduler	621	Greedy + Max-Heap	JS / Py

➤ Pattern Batches (JS + Python)

Pattern	LeetCode Numbers	Solution File
Sliding Window	76, 209, 424, 567, 904	JS / Py
Two Pointers	11, 15, 26, 42, 75, 88	JS / Py
Binary Search	33, 153, 162, 704	JS / Py
BFS	102, 200, 994, 542, 286, 815	JS / Py
Backtracking	39, 46, 51, 78, 79	JS / Py
Dynamic Programming	70, 198, 300, 322, 1143, 416	JS / Py

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📖 Quick Reference Links

• SQL Questions & Answers
• System Design Case Studies
• Machine Coding Questions
• DSA Cheat Sheet & Patterns
• Sorting & Searching Algorithms
• Design Patterns
• DevOps Interview Notes
• Kubernetes Interview Notes