Site: code.golf

Write shortest code to do something.  Existing problems broken up into categories.

Find all numbers with COND under VALUE

Some problems have a long version, usually meaning the shorter version has the possibility of having a better solution just printing the numbers instead of calculating them.

• Abundant Numbers - sum of proper divisors is greater than itself

• Abundant Numbers (Long)

• Emirp Numbers - find number that backwards and forwards is prime and different from each other

• Emirp Numbers (Long)

• Evil Numbers - number has even number of 1's in binary

• Evil Numbers (Long)

• Happy Numbers - continued summing of squares of digits will end at 1

• Happy Numbers (Long)

• Niven Numbers - number divisible by sum of digits

• Niven Numbers {Long)

• Odious Numbers - number has odd number of 1's in binary

• Odious Numbers (Long)

• Pernicious Numbers - number had prime numbers of 1's in binary

• Pernicious Numbers (Long)

• Prime Numbers

• Prime Numbers (Long)

• Smith Numbers - number is divisible by sum of digits of prime factors

• Vampire Numbers - number can be factored into two numbers such that factors have half as many digits as the number

Compute something for all numbers up to VALUE

• Collatz - find number of steps to 1

• Divisors - find all divisors of a number

• Fizz Buzz

• Fizz Buzz Bar Baz

• Leap Years - print leap years from 1800 to 2400

• Leyland Numbers - up to 100,000,000,000

• Ordinal Numbers

• Spelling Numbers

Print a sequence of numbers

Next output has dependency on previous output.

• Catalan Numbers - last number is 57 digits long

• Fibonacci

• Inventory Sequence

• Kolakoski Sequence

• Look and Say

• Lucky Numbers

• Pascal's Triangle

• Recamán

• Van Eck Sequence

Computation

Given primarily numerical inputs, perform the given computation

• Reverse Polish Notation - evaluate RPN expression

• Fractions - reduce a given fraction

• Intersection - compute the area of intersection of two boxes on a plane

• Jacobi Symbol

• Lucky Tickets - given number of digits and a base, compute number of tickets that meet a condition

• Repeating Decimals - given a fraction, print the decimal expansion, notating repeating digits

• Arabic to Roman

• ISBN - calculate checksum of ISBN number

• Time Distance - round seconds to closest larger unit

• Zodiac Signs - Date/time to zodiac sign

String Processing

Compute something on a string of text

• CSS Colors - Map colors names to hex values

• Emojify - convert emoticon to emoji

• Hexdump - mimic output of hexdump on string

• Levenshtein Distance - calculate number of edits between two strings

• Morse Encoder

• Pangram Grep

• Roman to Arabic

• United States - Map state names to state abbreviations

ASCII Art

Print lines of texts.  Output is usually fixed.  Usually the text has more computability than entries in string compression.

• ASCII Table - mimic output of 'man 7 ascii'

• Christmas Trees - trees made of asterisks (*)

• Cubes - wireframe cubes

• Diamonds - diamonds made of numbers

• Number Sprial - 10x10 grid from 0 to 99 in middle

• Sierpiński Triangle - printed with (▲)

• Rule 110

• Seven Segment - input varies

• Star Wars Opening Crawl - input varies

Computer Science

• brainfuck - execute brainfuck code and write output

• quine - printf("quine");

Complex Input

Input is 2D data in ASCII

• Proximity Grid - reachability analysis of given grids

• Game of Life - apply one step of Game of Life

• Maze - solve a given maze

• Sudoku

• Sudoku v2

• QR Decoder

Emoji processing

Input is strings with emoji (UTF8 characters)

• Poker - print what hand is given

• Rock Paper Scissors Spock Lizard

• Ten Pin Bowling

• Arrows

• Morse Decoder

• Musical Chords

String compression

Print lines of text, usually as part of a song.  No input, output always the same.

• 12 Days of Christmas

• 99 Bottles of Beer

• Tongue Twisters - woodchuck, Peter Piper, and Sally's seashells

Numeric Compression

Print numeric expansion of some constant.  Tests compression of data consisting of only 0-9, 1000 digits.

• Catalan's Constant

• Kolakoski Constant

• γ

• λ

• π

• τ

• φ

• √2

• 𝑒

Leaderboard

26-5-19

Derek increases his lead by submitting a new leading solution to Collatz.

Derek attempts a challenge to Factorial Factorization, but falls a little short.

Derek improves Factorial Factorization closing the gap by 14.

Richard T improved his Collatz solution, reducing Derek's lead to just 1.

Derek's hint of sscanf allows Richard to improve his Repeating Decimals solution by 7, but still trails by 4.

Richard T eliminates a loop and moves ahead by 8 on Divisors, taking the lead for the first time.

Derek improves on Factorial Factorization, but still trails by 9.

Derek finds a different way in Divisors and ties up everything.

Derek and Richard T tie on Fractions.

Derek trails in ISBN by 15

Derek increases the lead on Repeating Decimals to 10

Derek is uncontested in United States

Derek is uncontested in Zeckendorf Representation

Richard T takes back the lead by Zeckendorf Representation by 2.

Derek closes in on ISBN, only 2 away.

Derek opens a new front by announcing an attack on Lucky Tickets.  Richard T takes this opportunity to improve defense by 3 points, but Derek succeeds in blowing by with a 9 point lead.

Derek takes the largest lead so far getting a 46 point lead in Lucky Tickets.

Derek modulates his way to tying on ISBN.

Derek lands a heavy strike on Sierpinski Triangle with a 46 point lead.

Richard T retaliates with a 13 point lead on Sierpinski Triangle

Richard T makes a minor improvement to Sierpinski Triangle, still behind by 44.

Derek opens up more questions by taking on ASCII Table, ahead by 10 and Odious Numbers, trailing by 1.

Derek improves Sierpinski Triangle by 5

A new player has joined!!!!

Catch up on records.

Derek opens up several new fronts in the battle and takes a commanding lead.

Richard T uses a shorter type name to break the tie on Transpose Sentence.

Every trick I know for golfing

• code.golf specific tricks

  • #import<bits/stdc++.h> will make most of the standand libaries available

  • #import<ios> gets most C I/O functions, such as printf, sscanf, and atoi

  • __builtin_printf is available without any headers

• Use floating point constants to replace larger numbers, 1e4 instead of 1000

• Logical-and can sometimes be replaced by bitwise-and or multiplcation and logical-or and be replaced by bitwise-or or addition in some circumstances.

• The ternary operator (?:) and short-circuit of the logical-and (&&) and logical-or (||) can be used in control flow.

  • cond && printf("only print on true cond");

  • cond || printf("only print on false cond");

  • The ternary operator has an extension to allow an empty true statement

    • a?:c is the same as a?a:c

  • The comma operator can be used in the true branch to have multiple statements, but the false branch will need parens.

    • a?b1,b2:(c1,c2)

• Use as few print statements as possible.  If many are needed, capturing output stream or printf function pointer will save characters on subsequent calls to print statements.

  • • auto&o = std::cout  << "Hi";

    • auto*p = printf;

• Tadpole operators (-~ and ~-) to get value +/-1 with higher precedence than adding and subtracting

• Replace char literals with their ascii values.  65 instead of 'A'

• Integer condition checks

  • a != b is the same as a-b in bool context

  • a/b is non-zero when a > b, good for use in arithmetic operations without needing parens

  • a!=0 can be changed to just a

  • ~a will be 0 when a is -1, useful with sscanf return value

  • ~-a will be 0 when a is 1

• Looping checks

  • Putting increment/decrement in the loop condition to save a statement

  • Instead of looping 0 to N, go from N to 0

    • for (int i = 25; --i; );

  • printf returns the number or characters printed.  If the last printed is the longest to be printed, use the return value in the loop check.

  • sscanf will return -1 on failure.  Useful when working with multiple argv strings.

  • Crashing on a segmentation fault counts as a successful program end.  One way to do this is by iterating over argv until it crashes on a null string.  Calling main over and over with an incremented argv will traverse the array.

    • int main(int argc, char* argv[]) {
        char *c = *++argv;
        int x = atoi(c);
        main(argc, argv);
      }

• Loops

  • for(;cond;) is the same length as while(cond), but for has extra spots to put statements to save a semi-colon.

  • If the loop body only has one statement, the parens can be removed

  • Combine loops if possible to save characters.  Both nested and serial loops can be combined in various ways.

• Prime numbers, divisors

  • Using modulus operator (%) to find if a number is a divisor

  • All number have two divisors, 1 and itself.  Primes will only have those two.

  • Prime checks can happen either count up or count down.  If the first divisor found is the number itself, or 1, then it is prime.  Using a post decrement, the 1 can be made into a 0 for an easier check later.

  • To get prime factors of a number, the smallest divisor greater than 1 is a prime.  Each prime factor must be divided from the number, possibly multiple times, before finding the next factor.