Codebook

This is my C-language "book of code" for competitive programming problems. Thanks to the depth and breadth of competitive programming problems, this repository has become home to a diverse library including mathematical functions, data structures, and algorithms.

• Project Euler
• LeetCode

Why C?

C is a wonderful language because powerful abstractions come at an extremely low cost. I can take liberties with my implementations (such as runtime generics) while outperforming modern (bloated) alternatives, often by orders of magnitude. Plus C is readable, elegant, and beautiful (sometimes).

Constraints

• Adhere to the project style guide.
• Implement all final solutions following the C99 standard.
  • Assume that the English letter characters are ordered sequentially (i.e., no EBCDIC).
  • Assume that signed integer overflow is defined based on two's complement.

Dependencies

This repository depends on the GNU Multiple Precision Arithmetic Library (GMP), which is licensed under the GNU Lesser General Public License v3.0 (LGPL-3.0).

Project Euler

Id	Problem	Domain	Result	Implementation
1	Multiples of 3 or 5	Sequences	Sum	1 + 2 + 3 + 4 + ...
2	Even Fibonacci Numbers	Sequences	Sum	Fibonacci sequence
3	Largest Prime Factor	Number theory	Maximum	Trial division
4	Largest Palindrome Product	Number theory	Maximum	Palindromic number
5	Smallest Multiple	Number theory	Least common multiple	Euclidean algorithm
6	Sum Square Difference	Sequences	Difference	Square pyramidal number
7	10001st Prime	Number theory	Term	Sieve of Eratosthenes
8	Largest Product in a Series	Dynamic programming	Maximum	Sliding-window technique
9	Special Pythagorean Triplet	Geometry	Product	Euclid's formula
10	Summation of Primes	Number theory	Sum
11	Largest Product in a Grid	Dynamic programming	Maximum
12	Highly Divisible Triangular Number	Sequences	Term	Integer factorization
13	Large Sum	Arithmetic	Quotient	Floating-point arithmetic
14	Longest Collatz Sequence	Sequences	Term	Collatz conjecture
15	Lattice Paths	Combinatorics	Binomial coefficient	Binomial coefficient
16	Power Digit Sum	Arbitrary-precision arithmetic	Sum	Arbitrary-precision arithmetic
17	Number Letter Counts	Combinatorics	Count
18, 67	Maximum Path Sum	Dynamic programming	Maximum	Bottom-up approach
19	Counting Sundays	Combinatorics	Count
20	Factorial Digit Sum	Arbitrary-precision arithmetic	Sum
21	Amicable Numbers	Number theory	Sum	Amicable numbers
22	Names Scores	Sorting	Sum	Sorting algorithm
23	Non-Abundant Sums	Number theory	Sum	Abundant numbers
24	Lexicographic Permutations	Combinatorics	Permutation	Permutation
25	1000-digit Fibonacci Number	Sequences	Term number	Fibonacci sequence
26	Reciprocal Cycles	Number theory	Maximum	Full reptend prime
27	Quadratic Primes	Number theory	Product
28	Number Spiral Diagonals	Sequences	Sum	Arithmetic sequence
29	Distinct Powers	Number theory	Count
30	Digit Fifth Powers	Number theory	Sum
31	Coin Sums	Combinatorics	Partition	Partition function
32	Pandigital Products	Number theory	Sum	Pandigital number
33	Digit Cancelling Fractions	Number theory	Greatest common divisor
34	Digit Factorials	Combinatorics	Sum	Factorial
35	Circular Primes	Number theory	Count	Circular prime
36	Double-base Palindromes	Number theory	Sum	Radix
37	Truncatable Primes	Number theory	Sum	Truncatable prime
38	Pandigital Multiples	Number theory	Maximum
39	Integer Right Triangles	Geometry	Maximum
40	Champernowne's Constant	Number theory	Product	Champernowne constant
41	Pandigital Prime	Number theory	Maximum
42	Coded Triangle Numbers	Sequences	Count
43	Sub-string Divisibility	Number theory	Sum
44	Pentagonal Numbers	Sequences	Minimum	Pentagonal number
45	Triangular, Pentagonal, and Hexagonal	Sequences	Term	Hexagonal number
46	Goldbach's Other Conjecture	Number theory	Minimum
47	Distinct Primes Factors	Number theory	Term
48	Self Powers	Arbitrary-precision arithmetic	Modulus
49	Prime Permutations	Sequences	Terms
50	Consecutive Prime Sum	Number theory	Maximum
51	Prime Digit Replacements	Number theory	Minimum
52	Permuted Multiples	Combinatorics	Minimum
53	Combinatoric Selections	Combinatorics	Count
54	Poker Hands	Simulation	Count	Poker
55	Lychrel Numbers	Number theory	Count	Lychrel number
56	Powerful Digit Sum	Arbitrary-precision arithmetic	Maximum
57	Square Root Convergents	Arbitrary-precision arithmetic	Count	Continued fraction expansion
58	Spiral Primes	Sequences	Term number
59	XOR Decryption	Cryptography	Sum	Frequency analysis
60	Prime Pair Sets	Number theory	Minimum	Miller–Rabin primality test, Modular exponentiation, Exponentiation by squaring
61	Cyclical Figurate Numbers	Number theory	Sum	Polygonal number
62	Cubic Permutations	Number theory	Minimum	Multimap, Daniel J. Bernstein (djb2) hash algorithm
63	Powerful Digit Counts	Number theory	Count
64	Odd Period Square Roots	Algebra	Count
65	Convergents of e	Arbitrary-precision arithmetic	Count
66	Diophantine Equation	Arbitrary-precision arithmetic	Maximum	Pell's equation
68	Magic 5-gon Ring	Magic shapes	Maximum	Magic square
69	Totient Maximum	Number theory	Primorial	Euler's totient function
70	Totient Permutation	Number theory	Minimum
71	Ordered Fractions	Sequences	Term	Farey sequence
72	Counting Fractions	Number theory	Count	Totient summatory function
73	Counting Fractions in a Range	Sequences	Count
74	Digit Factorial Chains	Combinatorics	Count
75	Singular Integer Right Triangles	Geometry	Count
76	Counting Summations	Combinatorics	Partition
77	Prime Summations	Combinatorics	Term
78	Coin Partitions	Combinatorics	Term	Pentagonal number theorem
79	Passcode Derivation	Graph theory	Minimum	Adjacency matrix
80	Square Root Digital Expansion	Arbitrary-precision floating point arithmetic	Sum
81	Path Sum: Two Ways	Graph theory	Minimum path
82	Path Sum: Three Ways	Graph theory	Minimum path
83	Path Sum: Four Ways	Graph theory	Minimum path
84	Monopoly Odds	Simulation	Maxima	Blackman and Vigna's xoshiro256** algorithm
85	Counting Rectangles	Geometry	Area
86	Cuboid Route	Geometry	Minimum
87	Prime Power Triples	Number theory	Count	Hash set
89	Roman Numerals	Numeral systems	Difference	Roman numerals
91	Right Triangles with Integer Coordinates	Geometry	Count
92	Square Digit Chains	Number theory	Count

LeetCode

Id	Problem	Domain	Result	Implementation
7	Reverse Integer	Mathematics	Integer	math_reverse
8	String to Integer	Strings	Integer	atoll
9	Palindrome Number	Mathematics	Boolean	math_is_palindrome
12	Integer to Roman	String	Mathematics	roman_to_string_builder
13	Roman to Integer	Mathematics	Integer	roman_from_string_builder
23	Merge k Sorted Lists	Linked Lists	Linked List	PriorityQueue
28	Find the Index of the First Occurrence in a String	Strings	Index	strstr
29	Divide Two Integers	Mathematics	Quotient
31	Next Permutation	Array	Permutation	PermutationIterator
46	Permutations	Array	Permutation	PermutationIterator
50	Pow(x, n)	Mathematics	Power	pow
60	Permutation Sequence	Mathematics	Permutation	PermutationIterator
62	Unique Paths	Combinatorics	Binomial coefficient	binomial
69	Sqrt(x)	Mathematics	Square root	sqrt
75	Sort Colors	Sorting	Sort	qsort
77	Combinations	Backtracking	Matrix	CombinationIterator
150	Evaluate Reverse Polish Notation	Mathematics	Integer	rpn_evaluate
202	Happy Number	Mathematics	Boolean	SquareDigitChain
204	Count Primes	Mathematics	Count	Sieve, binary_search_rank
258	Add Digits	Mathematics	Digital root
263	Ugly Number	Mathematics	Boolean
273	Integer to English Words	Mathematics	String	words_to_string
367	Valid Perfect Square	Mathematics	Boolean	math_is_polygonal
650	2 Keys Keyboard	Mathematics	Sum	Sieve, factor_sum
744	Find Smallest Letter Greater Than Target	Binary search	Character	binary_search_min
2119	A Number After a Double Reversal	Mathematics	Boolean	math_reverse
2400	Number of Ways to Reach a Position After Exactly k Steps	Combinatorics	Binomial coefficient	mod_binomial_range
2427	Number of Common Factors	Mathematics	Count	gcd
2507	Smallest Value After Replacing With Sum of Prime Factors	Mathematics	Minimum	Sieve, factor_sum
2520	Count the Digits That Divide a Number	Mathematics	Count
2521	Distinct Prime Factors of a Product Array	Mathematics	Count	FactorIterator, Sieve
2544	Alternating Digit Sum	Mathematics	Sum
2550	Monkey Move	Combinatorics	Power	mod_pow