🧠 Data Structures & Algorithms

A comprehensive, well-organized collection of 130+ solutions to data structures and algorithms problems — spanning core CS fundamentals, competitive programming patterns, and real-world interview questions.

Built as a living reference for algorithm design, complexity analysis, and problem-solving fluency in C++, Java, and JavaScript.

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📖 Table of Contents

#	Topic	Problems	Highlights
1	Trees & BSTs	42	Traversals, Views, LCA, Serialize/Deserialize, Largest BST
2	Graphs	19	Dijkstra, Bellman-Ford, Floyd-Warshall, SCC, MST, Topological Sort
3	Dynamic Programming	15	Knapsack variants, Grid DP, LCS, Coin Change, Paint Houses
4	Binary Search	12	Rotated Arrays, Peak Finding, Matrix Median, Nth Root
5	Recursion & Backtracking	10	N-Queens, Rat in a Maze, Combination Sum, Word Square
6	Interview Problems	10	Real OA/interview problems with solutions
7	Trie	7	Implementations, Max XOR, Distinct Substrings
8	Linked Lists	3	Reverse SLL/DLL, Flatten Multi-level List
9	Stacks	3	Next/Previous Greater & Smaller Elements, Min Stack
10	Sliding Window	1	Permutation in String
11	Greedy	2	Demand-Supply Pattern, Maximum Earning
12	Cyclic Sort	2	Cycle Sort, Find Missing Number
13	Arrays	1	Maximum Frequency in Range
14	Math	1	Binary Exponentiation
15	JavaScript Polyfills	1	Native method re-implementations

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🌲 Trees & Binary Search Trees

Extensive coverage of tree-based problems using both iterative and recursive approaches.

Binary Tree Fundamentals

Problem	File
DFS Traversals (Pre/In/Post — Recursive & Iterative)	tree_traversal.cpp, tree_traversals.cpp
Level Order / BFS Traversal	tree_traversals.cpp
Height of Binary Tree	height_of_tree.cpp
Diameter of Binary Tree	diameter_of_tree.cpp
Balanced Binary Tree Check	balanced_binary_tree.cpp
Invert Binary Tree	invert_binary_tree.cpp
Count Nodes in Complete Tree	count_nodes_in_complete_tree.cpp
Check Complete Binary Tree	check_complete_tree.cpp
Construct Binary Tree from Traversals	construct_binary_tree.cpp
Count Connected Components (Number of Islands)	connected_components.cpp

Tree Views & Orders

Problem	File
Left View	left_view.cpp
Right View	right_view.cpp
Top View	top_view.cpp
Bottom View	bottom_view.cpp
Vertical Order Traversal	vertical_order_traversal.cpp
Boundary Traversal	boundry_traversal.cpp
Maximum Width	maximum_width.cpp

Advanced Tree Problems

Problem	File
Lowest Common Ancestor	lowest_common_ancestor.cpp
Maximum Path Sum	maximum_path_sum.cpp
Longest Increasing Path in Tree	maximum_leanage_path.cpp
Longest Consecutive Path	longest_consecutive_path.cpp
Longest Univalue Path	longest_univalue_path.cpp
Flatten to Linked List (Preorder)	flatten_binary_tree_preorder.cpp
Flatten to Linked List (Inorder)	flatten_binary_tree_inorder.cpp
Find Duplicate Subtrees	find_duplicate_trees.cpp
Expression Tree Evaluation	expression_tree.cpp
Serialize / Deserialize Tree	TreeCodec.java

Binary Search Trees

Problem	File
Search in BST	search_in_bst.cpp
Insert Node in BST	insert_node_bst.cpp
Delete Node in BST	delete_in_bst.cpp
Construct BST from Preorder	construct_bst.cpp
Validate BST	validate_bst.cpp
LCA in BST	lca_in_bst.cpp
Floor in BST	floor_in_bst.cpp
Ceil in BST	ceil_in_bst.cpp
Recover BST	recover_bst.cpp
Largest BST in Binary Tree	largestBST_in_tree.cpp
BST Iterator	BSTIterator.java
BST Bidirectional Iterator	BSTBidirectionalIterator.java
Two Sum in BST	TwoSum.java
BST Codec (Serialize/Deserialize)	BSTCodec.java

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📈 Graphs

Covers all major graph algorithms — shortest paths, cycle detection, topological ordering, and connectivity.

Problem	Algorithm / Technique	File
Build Adjacency List	Graph Representation	build_graph.cpp
Print All Paths	DFS	print_all_paths.cpp
Detect Cycle (Undirected — BFS)	BFS + Parent Tracking	detect_cycle_bfs.cpp
Detect Cycle (Undirected — DFS)	DFS + Parent Tracking	detect_cycle_dfs.cpp
Detect Cycle (Directed)	DFS + Recursion Stack	detect_cycle_directed.cpp
Bipartite Graph Check	BFS/DFS Coloring	bipartite_graph.cpp
Topological Sort	DFS-based	topological_sort.cpp
Kahn's Algorithm	BFS Topological Sort	kahn_algorithm.cpp
Shortest Path (Undirected)	BFS	shortest_distance_undirected.cpp
Shortest Path (DAG)	Topological Sort + Relaxation	shortest_path_dag.cpp
Dijkstra's Algorithm	Min-Heap / Priority Queue	dijkstra.cpp
Bellman-Ford Algorithm	Edge Relaxation	bellman_ford.cpp
Floyd-Warshall Algorithm	All-Pairs Shortest Path	floyd_warshall.cpp
Prim's MST ⏳	Greedy + Priority Queue	prims_mst.cpp
Disjoint Set Union (by Rank)	Union-Find	dsu_rank.cpp
Strongly Connected Components	Kosaraju's Algorithm	strongly_connected_components.cpp
Rotten Oranges	Multi-source BFS	Rotten_oranges.cpp
Number of Distinct Islands	DFS + Hashing	number_of_distinct_islands.cpp
Word Ladder ⏳	BFS Level-order	word_ladder.cpp

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💡 Dynamic Programming

Organized by sub-pattern for easy reference.

Grid / Matrix DP

Problem	File
Minimum Path Sum (LC #64)	manimum_path.cpp
Triangle Minimum Path (LC #120)	triangle.cpp
Unique Paths (LC #62)	variant1.cpp
Unique Paths with Obstacles (LC #63)	variant2.cpp
Cherry Pickup II — Max Fruits with Two Players (LC #1463)	3Dgrid.cpp

Subsequences & Knapsack

Problem	File
0/1 Knapsack	knapsack.cpp
Unbounded Knapsack	unbounded_knapsack.cpp
Coin Change — Minimum Coins (LC #322)	minimum_coins.cpp
Subset Sum Problem	find_target_sum.cpp
Target Sum — Assign +/- Signs (LC #494)	assign_sign.cpp

Strings

Problem	File
Longest Common Subsequence	longest_common_subsequences.cpp

Other DP

Problem	File
Ninja Training / Paint Houses — Memoization	memoization.cpp
Ninja Training / Paint Houses — Tabulation	tabulation.cpp
Frog Jump with K Steps	DP-3.cpp

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🔍 Binary Search

All problems leverage the binary search paradigm on sorted or monotonic data.

Problem	File
Iterative Binary Search	binary_search.cpp
Recursive Binary Search	recursive_binary_search.cpp
Lower Bound	lower_bound.cpp
Upper Bound	upper_bound.cpp
First & Last Occurrence	first_and_last_occurance.cpp
Search in Sorted Rotated Array	search_In_sorted_rotated_array.cpp
Find Peak Element (1D)	find_peak_element.cpp
Find Peak Element (2D Matrix)	peak_element_matrix.cpp
Single Non-Duplicate in Sorted Array	single_non_duplicate.cpp
Nth Root of Integer	nth_root.cpp
Square Root with Precision	precise_sqrt_number.cpp
Median in Row-wise Sorted Matrix	median_in_matrix.cpp

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🔄 Recursion & Backtracking

Problem	File
Combination Sum	combination_sum.cpp
Combination Sum II	combination_sum_2.cpp
Unique Permutations	unique_permutations.cpp
Palindrome Partitioning	palindrome_partitioning.cpp
N-Queens	n_queens.cpp
N-Queens (2nd Approach)	n_queens_2_approach.cpp
Rat in a Maze	rat_in_maze.cpp
Word Square	word_square.cpp
Print First Subset with Sum K	print_first_result.cpp
Merge Sort	merge_sort.cpp

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🏢 Interview Problems

Real coding assessment and interview questions with clean, documented solutions.

Problem	Description
Waste Reduction	Choose optimal container sets to minimize waste
Apartment Hunting	Find the best apartment location minimizing max distance to facilities
Conference Room Booker	Schedule meetings across conference rooms
Course Allotment	Assign courses to students optimally
Task Allotment	Distribute tasks efficiently
Organization Restructuring	Tree-based org hierarchy problem
Piano Player	Finger placement optimization
String Buddies	String transformation / matching
File Size	File system size computation
Volunteers	Volunteer assignment problem

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🔤 Trie

Problem	File
Trie Implementation (C++)	TrieImpl1/TrieImpl.cpp
Trie Implementation (Java — v1)	TrieImpl1/TrieImpl.java
Trie Implementation (Java — v2)	TrieImpl2/TrieImpl.java
Count Distinct Rows in Binary Matrix	Problems/CountDistinctRowsInBinaryMatrix/solution.cpp
Longest Word with All Prefixes	Problems/LongestWordWithAllPrefixes/Solution.java
Maximum XOR	Problems/MaximumXOR/solution.cpp
Number of Distinct Substrings	Problems/NumberOfDistinctSubstrings/Solution.java

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🔗 Linked Lists

Problem	File
Reverse Singly Linked List	reverseLL.cpp
Reverse Doubly Linked List	reverseDLL.cpp
Flatten Multi-level Linked List	flatten_linked_list.cpp

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📚 Stacks

Problem	File
Previous & Next Greater Element	find_pge_and_nge.cpp
Previous & Next Smaller Element	find_pse_and_nse.cpp
Min Stack	minStack.cpp

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🪟 Sliding Window

Problem	File
Permutation in String (LC #567)	stringMatching.cpp

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💰 Greedy

Problem	File
Demand-Supply Pattern (LC 659)	DemandSupplyPattern/Leetcode659.cpp
Maximum Earning	MaximumEarning/solution.cpp

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🔢 Cyclic Sort

Problem	File
Cycle Sort	cycleSort.cpp
Find Missing Number	findMissingNumber.cpp

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📐 Arrays

Problem	File
Maximum Appearing Element in Ranges (Prefix Sum)	MaximumFreqInRange.cpp

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➗ Math

Problem	File
Binary Exponentiation (Fast Power)	binary_exponentiation.cpp

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🌐 JavaScript Polyfills

Problem	File
Native Method Re-implementations	jsCode.js

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🗂️ Repository Structure

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├── Arrays/                     # Array-based problems
├── BinarySearchAlgorithms/     # Binary search variants & applications
├── CyclicSortProblems/         # Cyclic sort pattern
├── DynamicProgramming/         # DP organized by sub-pattern
│   ├── Grid/
│   ├── PaintHouses/
│   ├── Strings/
│   └── Subsequences/
├── Graphs/                     # All major graph algorithms
├── GreedyProblems/             # Greedy approach problems
├── InterviewProblems/          # Real interview & OA questions
│   ├── ApartmentHunting/
│   ├── ConferenceRoomBooker/
│   ├── WasteReduction/
│   └── ...
├── JavaScript Polyfills/       # JS native method polyfills
├── LinkedList/                 # Linked list problems
├── MathAlgorithms/             # Number theory & math
├── Recursion/                  # Backtracking & recursion
├── SlidingWindow/              # Sliding window technique
├── Stacks/                     # Stack-based problems
├── TreesAlgorithms/            # Binary trees & BSTs
│   └── BinarySearchTrees/
├── Trie/                       # Trie implementations & problems
│   ├── TrieImpl1/
│   ├── TrieImpl2/
│   └── Problems/
└── README.md

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🛠️ Tech Stack

Language	Use Case
C++	Primary language — STL, templates, memory-efficient solutions
Java	BST iterators, Trie problems, Tree serialization
JavaScript	Polyfills and language internals

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🚀 How to Run

# C++ (compile & run)
g++ -std=c++17 -o solution <file>.cpp && ./solution

# Java
javac <File>.java && java <File>

# JavaScript
node <file>.js

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Continuously growing — new problems and patterns added regularly.