🚀 Dhruv's Competitive Programming & DSA Library

A curated, production-grade, and highly-optimized C++ library containing core algorithms, data structures, and standard boilerplate templates designed for Competitive Programming, online judges (Codeforces, Codechef, AtCoder), and coding interviews.

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📚 Theory, Formulas & Cheatsheets

All conceptual notes, proofs, and formula sheets are organized under 0_theory/. Each topic below links directly to its notes or subfolder.

📖 Algorithm-Specific Theory Guides

Subject / Topic	Core Concepts Covered
📦 Arrays & Range Queries	Prefix sums, 2D prefix sums, suffix sums, difference arrays, subarray sum, two pointers, sliding window, Kadane's algorithm
🔢 Mathematics & Number Theory	Sieve of Eratosthenes, smallest prime factor (SPF), prime factorization, divisors, factorials, modular inverse, binary exponentiation
🔍 Binary Search	Standard binary search, lower/upper bound, binary search on integer answer space, binary search on decimals
🔀 Sorting Algorithms	Merge sort (divide & conquer), quick sort (partition strategy & pivot selection)
⚡ Bit Manipulation	Count set bits (Kernighan's), lowest/highest set & unset bit positions, subset enumeration via bitmasking
🌲 Graphs & Trees	DFS, BFS, node levels, Euler tour (in/out times), parent precomputation, subtree sizes, node height, tree diameter, ancestor queries
🛠️ Miscellaneous & Templates	Fast I/O setup, GNU PBDS ordered_set, sort map by values

📐 Conceptual Math & Reference Sheets

Subject / Topic	Core Concepts Covered
📐 Mathematics Formulas	Arithmetic, algebraic, geometric, volume, and perimeter formulas
📍 Coordinate Geometry	Midpoints, distances, triangle area via coordinates
🪵 Logarithms	Logarithmic identities, change of base, digit counting tricks
🎲 Combinatorics	Permutations, combinations, circular arrangements, Stars & Bars
📈 Probability	Probability axioms, conditional probability, expected value, linearity
🔢 Modular Arithmetic	Modular add/sub/mul/div rules, modular inverse, Fermat's Little Theorem
⚡ Fermat's Little Theorem	Theorem statement, modular inverse via binary exponentiation, C++ template
🧮 GCD & LCM	Euclidean algorithm, LCM–GCD relation, extended GCD properties
📏 Divisibility Rules	Quick primality checks via divisibility rules for primes
🧿 Euler's Totient	$\phi(n)$ product formula, Euler's Theorem, exponent reduction, power towers
🔤 ASCII Table	ASCII decimal mappings, char arithmetic, string conversion utilities

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📂 Code Index

Click any filename to view the standalone, production-ready C++ implementation.

📦 1. Arrays & Range Queries

#	Algorithm / Technique	File
1	Prefix Sum Array	1_arrays/1_prefix_sum.cpp
2	2D Prefix Sum Matrix	1_arrays/2_2d_prefix_sum.cpp
3	Suffix Sum Array	1_arrays/3_suffix_sum.cpp
4	Difference Array	1_arrays/4_difference_array.cpp
5	Subarray Sum Equals K	1_arrays/5_subarray_sum.cpp
6	Two Pointers Technique	1_arrays/6_two_pointers.cpp
7	Sliding Window Max Sum	1_arrays/7_sliding_windows.cpp
8	Kadane's Algorithm (Max Subarray)	1_arrays/8_kadane_algorithm.cpp

🔢 2. Mathematics & Number Theory

#	Algorithm / Technique	File
1	Sieve of Eratosthenes	2_math/1_sieve_of_eratosthenes.cpp
2	Sieve — Smallest Prime Factor (SPF)	2_math/2_sieve_smallest_prime_factor.cpp
3	Distinct Prime Factorization	2_math/3_prime_factors.cpp
4	Efficient Factorization via SPF	2_math/4_efficient_prime_factor_using_spf.cpp
5	Smallest Prime Factor (Single)	2_math/5_smallest_prime_factor.cpp
6	Prime Check (Trial Division)	2_math/6_prime_check.cpp
7	Divisors / Factors of a Number	2_math/7_factors_of_number.cpp
8	Factorial with Modulo	2_math/8_factorial.cpp
9	Inverse Factorial (Fermat's LT)	2_math/9_inverse_factorial.cpp
10	Optimized nCr Calculations	2_math/10_optimised_ncr.cpp
11	Binary Exponentiation	2_math/11_binary_exponentiation.cpp
12	nCr Simple Formula	2_math/12_ncr.cpp
13	Legendre's Formula (Power of p in N!)	2_math/13_power_of_x_in_factorial.cpp
14	Power of x in N	2_math/14_power_of_x_in_n.cpp

🔍 3. Binary Search

#	Algorithm / Technique	File
1	Standard Binary Search	3_binary_search/1_binary_search.cpp
2	Lower Bound	3_binary_search/2_lower_bound.cpp
3	Upper Bound	3_binary_search/3_upper_bound.cpp
4	Binary Search on Answers (Integer)	3_binary_search/4_binary_search_on_answers.cpp
5	Binary Search on Answers (Decimal)	3_binary_search/5_binary_search_on_decimals.cpp

🔀 4. Sorting Algorithms

#	Algorithm / Technique	File
1	Merge Sort	4_sorting/1_merge_sort.cpp
2	Quick Sort	4_sorting/2_quick_sort.cpp

⚡ 5. Bit Manipulation

#	Algorithm / Technique	File
1	Count Set Bits (Kernighan's Algorithm)	5_bit_manipulation/1_count_the_set_bits.cpp
2	Lowest Set Bit Position	5_bit_manipulation/2_lowest_set_bit_position.cpp
3	Highest Set Bit Position	5_bit_manipulation/3_highest_set_bit_position.cpp
4	Lowest Unset Bit Position	5_bit_manipulation/4_lowest_unset_bit_position.cpp
5	Highest Unset Bit Position	5_bit_manipulation/5_highest_unset_bit_position.cpp
6	Highest Unset Bit (Significant Bits)	5_bit_manipulation/6_highest_unset_bit_among_significant_bits.cpp
7	Generate All Subsets via Bitmasking	5_bit_manipulation/7_generate_all_subset_using_bitmasking.cpp

🌲 6. Graphs & Trees

#	Algorithm / Technique	File
1	Precompute Parent of Every Node	7_trees/1_get_the_parent_of_the_node.cpp
2	Count Children for Every Node	7_trees/2_number_of_children_for_a_node.cpp
3	Find Subtree Size	7_trees/3_find_subtree_size.cpp
4	Farthest Leaf Node (Node Height)	7_trees/4_farthest_leaf_node_inside_subtree.cpp
5	Diameter of a Tree	7_trees/5_diameter_of_tree.cpp
6	Ancestor Query in O(1)	7_trees/6_ancestor_query.cpp
7	Depth First Search (DFS)	7_trees/7_depth_first_search.cpp
8	Breadth First Search (BFS)	7_trees/8_breadth_first_search.cpp
9	Find Level of Every Node	7_trees/9_find_level_of_every_node.cpp
10	DFS Entry / Exit Timers (Euler Tour)	7_trees/10_in_time_out_time.cpp

🛠️ 7. Miscellaneous & Boilerplate

#	Algorithm / Technique	File
1	Competitive Programming Boilerplate (Fast I/O + PBDS)	8_misc/1_boilerplate.cpp
2	Sort std::map by Values	8_misc/2_sort_map_by_values.cpp

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💻 Quick Start

Note

Ensure your compiler supports C++17 or above.

Compile

g++ -std=c++17 -O2 1_arrays/1_prefix_sum.cpp -o solution

Run

./solution < input.txt > output.txt

Compile & Run (one-liner)

g++ -std=c++17 -O2 2_math/11_binary_exponentiation.cpp -o sol && ./sol