Describe how to create fork in README

.template.lua

@@ -1,3 +1,5 @@
+-- Description
+--
 -- Solution --------------------------------------------------------------------
 function f()
 	-- Your implementation here

01_maximum.lua

@@ -1,3 +1,5 @@
+-- Implement a function to return the largest value in a list.
+--
 -- Solution --------------------------------------------------------------------
 function maximum(list)
 	-- Your implementation here

02_leap_years.lua

@@ -1,3 +1,6 @@
+-- Implement is_leap_year() below, returning whether the given year is
+-- a leap year according to the Gregorian calendar.
+--
 -- Solution --------------------------------------------------------------------
 function is_leap_year(year)
 	-- Your implementation here

03_hamming_distance.lua

@@ -1,3 +1,8 @@
+-- The hamming distance is the number of positions in which two
+-- strings differ, and is used to measure how similar strings are.
+-- Implement the hamming_distance() function below to calculate this;
+-- you may assume that the strings are of equal length.
+--
 -- Solution --------------------------------------------------------------------
 function hamming_distance(str1, str2)
 	-- Your implementation here

04_resistor_colours.lua

@@ -1,18 +1,8 @@
+-- Write a function to determine the resistance (in ohms) of a given
+-- three-part resistor colour code.  The colour code is passed as a
+-- list of strings.
+--
 -- Solution --------------------------------------------------------------------
--- Give the colours whatever values are convenient
-black = undefined
-brown = undefined
-red = undefined
-orange = undefined
-yellow = undefined
-green = undefined
-blue = undefined
-violet = undefined
-grey = undefined
-white = undefined
-gold = undefined
-silver = undefined
-
 function decode_resistance(colours)
 	-- Your implementation here
 end
@@ -22,27 +12,27 @@ end
 local luaunit = require("luaunit.luaunit")
 
 function test_violet_orange_black_is_73_ohms()
-	local resistance = decode_resistance({violet, orange, black})
+	local resistance = decode_resistance({"violet", "orange", "black"})
 	luaunit.assertEquals(resistance, 73)
 end
 
 function test_brown_green_black_is_15_ohms()
-	local resistance = decode_resistance({brown, green, black})
+	local resistance = decode_resistance({"brown", "green", "black"})
 	luaunit.assertEquals(resistance, 15)
 end
 
 function test_green_blue_orange_is_56_kiloohms()
-	local resistance = decode_resistance({green, blue, orange})
+	local resistance = decode_resistance({"green", "blue", "orange"})
 	luaunit.assertEquals(resistance, 56000)
 end
 
 function test_white_yellow_yellow_is_940_kiloohms()
-	local resistance = decode_resistance({white, yellow, yellow})
+	local resistance = decode_resistance({"white", "yellow", "yellow"})
 	luaunit.assertEquals(resistance, 940000)
 end
 
 function test_orange_red_silver_is_320_milliohms()
-	local resistance = decode_resistance({orange, red, silver})
+	local resistance = decode_resistance({"orange", "red", "silver"})
 	luaunit.assertEquals(resistance, 0.32)
 end
 

05_greatest_common_divisor.lua

@@ -1,3 +1,9 @@
+-- The greatest common divisor (GCD) of two numbers is, as the name
+-- suggests, the largest number which evenly divides both.  Implement
+-- the function below to calculate this.  It's recommended that you
+-- use Euclid's algorithm but feel free to use another approach if you
+-- want.
+--
 -- Solution --------------------------------------------------------------------
 function greatest_common_divisor(x, y)
 	-- Your implementation here

06_prime_numbers.lua

@@ -1,3 +1,5 @@
+-- Write a function to determine whether a given number is prime.
+--
 -- Solution --------------------------------------------------------------------
 function is_prime(x)
 	-- Your implementation here

07_palindromes.lua

@@ -1,3 +1,7 @@
+-- Implement is_palindrome(), which should return whether the passed
+-- string is palindromic (i.e the same forwards as it is backwards).
+-- Ignore non-letters and case.
+--
 -- Solution --------------------------------------------------------------------
 function is_palindrome(str)
 	-- Your implementation here

08_anagrams.lua

@@ -1,3 +1,7 @@
+-- Implement the is_anagram() function below, so that it returns true if
+-- the two passed strings are anagrams of each other.  Any non-
+-- alphabetical characters in the string should be ignored.
+--
 -- Solution --------------------------------------------------------------------
 function is_anagram(str1, str2)
 	-- Your implementation here

09_queen_threats.lua

@@ -1,3 +1,8 @@
+-- Implement the function is_queen_threat() below.  It should return
+-- true if the queen is threatening the pawn and false otherwise.  The
+-- coordinates are as given as file (A-H), rank (1-8) pairs such as B3
+-- and D7.
+--
 -- Solution --------------------------------------------------------------------
 function is_queen_threat(queen_position, pawn_position)
 	-- Your implementation here

10_hexadecimal.lua

@@ -1,3 +1,6 @@
+-- Write a function to return the hexadecimal representation (in a
+-- string) of a number.  Use lowercase a to f.
+--
 -- Solution --------------------------------------------------------------------
 function hexadecimal(x)
 	-- Your implementation here

11_fibonacci_numbers.lua

@@ -1,3 +1,5 @@
+-- Write a function to calculate the nth fibonacci number.
+--
 -- Solution --------------------------------------------------------------------
 function nth_fibonacci_number(n)
 	-- Your implementation here

12_balanced_brackets.lua

@@ -1,3 +1,7 @@
+-- Implement is_balanced(), which should return true or false depending
+-- on whether the brackets in the input string are balanced,
+-- i.e. there is a closing bracket for each opening one.
+--
 -- Solution --------------------------------------------------------------------
 function is_balanced(input)
 	-- Your implementation here

13_prime_sieve.lua

@@ -0,0 +1,43 @@
+-- Write a function which takes a limit and returns a list of every
+-- prime number below that limit.  It is recommended that you use the
+-- "Sieve of Eratosthenes" algorithm, but you can try a different
+-- prime sieve algorithm if you want.
+--
+-- Solution --------------------------------------------------------------------
+function lesser_primes(limit)
+	-- Your implementation here
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+function test_primes_below_2048()
+	local primes = {
+		2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71,
+		73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151,
+		157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233,
+		239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317,
+		331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419,
+		421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503,
+		509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607,
+		613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701,
+		709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811,
+		821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911,
+		919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997, 1009, 1013, 1019,
+		1021, 1031, 1033, 1039, 1049, 1051, 1061, 1063, 1069, 1087, 1091, 1093, 1097,
+		1103, 1109, 1117, 1123, 1129, 1151, 1153, 1163, 1171, 1181, 1187, 1193, 1201,
+		1213, 1217, 1223, 1229, 1231, 1237, 1249, 1259, 1277, 1279, 1283, 1289, 1291,
+		1297, 1301, 1303, 1307, 1319, 1321, 1327, 1361, 1367, 1373, 1381, 1399, 1409,
+		1423, 1427, 1429, 1433, 1439, 1447, 1451, 1453, 1459, 1471, 1481, 1483, 1487,
+		1489, 1493, 1499, 1511, 1523, 1531, 1543, 1549, 1553, 1559, 1567, 1571, 1579,
+		1583, 1597, 1601, 1607, 1609, 1613, 1619, 1621, 1627, 1637, 1657, 1663, 1667,
+		1669, 1693, 1697, 1699, 1709, 1721, 1723, 1733, 1741, 1747, 1753, 1759, 1777,
+		1783, 1787, 1789, 1801, 1811, 1823, 1831, 1847, 1861, 1867, 1871, 1873, 1877,
+		1879, 1889, 1901, 1907, 1913, 1931, 1933, 1949, 1951, 1973, 1979, 1987, 1993,
+		1997, 1999, 2003, 2011, 2017, 2027, 2029, 2039
+	}
+	luaunit.assertEquals(lesser_primes(2048), primes)
+end
+
+os.exit(luaunit.LuaUnit.run())

14_vigenere.lua

@@ -0,0 +1,64 @@
+-- The Vigenère cipher is a way to encrypt text, where a key is
+-- repeated for the length of the plaintext and the alphabetical
+-- position of the keyword letter determines the amount the letter of
+-- the plaintext is shifted by.  For example, for plaintext "FOO" and
+-- key "BAR", the first letter of the cipher text would be G, the
+-- result of shifting the letter F (first letter of the plaintext)
+-- over by 1 (the zero-based alphabetical position of B, first letter
+-- of the key).
+--
+-- Implement a function to encode a message with a given keyword.  The
+-- message should be converted to upper-case and any non-alphabetical
+-- characters should be discarded.
+--
+-- Solution --------------------------------------------------------------------
+local a_value = 65
+
+function apply_shift(letter, shift)
+	local shifted = (letter - a_value + shift) % 26
+	return a_value + shifted
+end
+
+function vigenere_encode(plaintext, keyword)
+	local key = {}
+	for i = 1, #keyword do
+		local shift = string.byte(keyword, i) - a_value
+		table.insert(key, shift)
+	end
+
+	plaintext = string.gsub(string.upper(plaintext), "%A+", "")
+	ciphertext = ""
+	for i = 1, #plaintext do
+		local letter = string.byte(plaintext, i)
+		local shift = key[(i - 1) % #key + 1]
+		local shifted = apply_shift(letter, shift)
+		ciphertext = ciphertext .. string.char(shifted)
+	end
+
+	return ciphertext
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+function test_encoding_of_foo_with_key_BAR()
+	luaunit.assertEquals(vigenere_encode("FOO", "BAR"), "GOF")
+end
+
+function test_encoding_of_the_quick_brown_fox_with_key_JUMPSOVER()
+	local plaintext = "The quick brown fox"
+	local key = "JUMPSOVER"
+	local expected = "CBQFMWXOSAIICXCS"
+	luaunit.assertEquals(vigenere_encode(plaintext, key), expected)
+end
+
+function test_encoding_longer_phrase_with_key_LEAR()
+	local plaintext =
+		"They dined on mince and slices of quince, which they ate with a runcible spoon."
+	local key = "LEAR"
+	local expected = "ELEPOMNVOSNDTRCVLRDJWMCVDSFHFMNTPAHZNLTYPCAKPAIKSERLYGISWISGZSN"
+	luaunit.assertEquals(vigenere_encode(plaintext, key), expected)
+end
+
+os.exit(luaunit.LuaUnit.run())

15_run_length_encoding.lua

@@ -0,0 +1,28 @@
+-- Run length encoding is a simple data compression technique where a
+-- "run" of the same value is replaced with a count and a single copy.
+-- In this exercise we will use the notation "#<count>:<value>" to
+-- indicate such a run; however, this should only be put into the
+-- output if it is strictly shorter than the string it is replacing.
+-- The input will consist only of alphanumeric characters.
+--
+-- Solution --------------------------------------------------------------------
+function run_length_encode(input)
+	-- Your implementation here
+end
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+function test_encoding_of_aaaaaaaa22bbbbbbssssfffffff67eee66666asdfff()
+	local input = "aaaaaaaa22bbbbbbssssfffffff67eee66666asdfff"
+	local expected = "#8:a22#6:bssss#7:f67eee#5:6asdfff"
+	luaunit.assertEquals(run_length_encode(input), expected)
+end
+
+function test_encoding_of_wwwwwfffff1223566666666bbbbbbbbbbb78b99asasdfbnfasdafffffff99()
+	local input = "wwwwwfffff1223566666666bbbbbbbbbbb78b99asasdfbnfasdafffffff99"
+	local expected = "#5:w#5:f12235#8:6#11:b78b99asasdfbnfasda#7:f99"
+	luaunit.assertEquals(run_length_encode(input), expected)
+end
+
+os.exit(luaunit.LuaUnit.run())

16_postfix.lua

@@ -0,0 +1,47 @@
+-- Postfix notation is an alternative to the normal "infix" notation
+-- used in mathematical expressions.  Instead of writing the operator
+-- between the operands, the operator comes after them.  For example,
+-- "1 + 2" is notated as "1 2 +".  This removes the need for operator
+-- precedence and parentheses: rather than having to resolve the
+-- ambiguity of an expression like "1 + 2 * 3" with convention or
+-- parentheses, the evaluation order is explicit -- multiplication-
+-- first is "1 2 3 * +" and addition-first is "1 2 + 3 *".
+--
+-- As well as this notational convenience, postfix can be easily
+-- evaluated using a stack.  Whenever an operand is encountered, the
+-- value is pushed onto the stack, and whenever an operator is
+-- encountered, two values are popped from the stack and the result of
+-- the operation is pushed on in their place.  Finally, the value left
+-- on the top of the stack is the result of the operation.
+--
+-- Write a function that will evaluate a postfix expression and return
+-- the result.  You can assume that the expression is valid, and not
+-- worry about handling error cases.  The operators will be "+", "-",
+-- "*" and "/".
+--
+-- Solution --------------------------------------------------------------------
+function evaluate_postfix(expression)
+	-- Your implementation here
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+function test_1_2_plus_3_times_is_9()
+	luaunit.assertEquals(evaluate_postfix("1 2 + 3 *"), 9)
+end
+
+function test_1_2_3_times_plus_is_7()
+	luaunit.assertEquals(evaluate_postfix("1 2 3 * +"), 7)
+end
+
+function test_4_6_plus_5_divide_2_1_minus_minus_is_1()
+	luaunit.assertEquals(evaluate_postfix("4 6 + 5 / 2 1 - -"), 1)
+end
+
+function test_12_2_times_6_divide_10_times_2_plus_is_42()
+	luaunit.assertEquals(evaluate_postfix("12 2 * 6 / 10 * 2 +"), 42)
+end
+
+os.exit(luaunit.LuaUnit.run())

17_prime_factors.lua

@@ -0,0 +1,50 @@
+-- Write a function which determines the prime factors of a given
+-- number, returning them in a list.  You may assume that none of the
+-- prime factors are above 10000
+--
+-- Solution --------------------------------------------------------------------
+function prime_factors(n)
+	-- Your implementation here
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+function test_prime_factors_of_42()
+	luaunit.assertItemsEquals(prime_factors(42), {2, 3, 7})
+end
+
+function test_prime_factors_of_70()
+	luaunit.assertItemsEquals(prime_factors(70), {2, 5, 7})
+end
+
+function test_prime_factors_of_253()
+	luaunit.assertItemsEquals(prime_factors(253), {11, 23})
+end
+
+function test_prime_factors_of_245()
+	luaunit.assertItemsEquals(prime_factors(245), {5, 7, 7})
+end
+
+function test_prime_factors_of_36()
+	luaunit.assertItemsEquals(prime_factors(36), {2, 2, 3, 3})
+end
+
+function test_prime_factors_of_1337()
+	luaunit.assertItemsEquals(prime_factors(1337), {7, 191})
+end
+
+function test_prime_factors_of_4321()
+	luaunit.assertItemsEquals(prime_factors(4321), {29, 149})
+end
+
+function test_prime_factors_of_57812834()
+	luaunit.assertItemsEquals(prime_factors(57812834), {2, 29, 113, 8821})
+end
+
+function test_prime_factors_of_8894220()
+	luaunit.assertItemsEquals(prime_factors(8894220), {2, 2, 3, 5, 271, 547})
+end
+
+os.exit(luaunit.LuaUnit.run())

18_towers_of_hanoi.lua

@@ -0,0 +1,81 @@
+-- The Towers of Hanoi is a mathematical puzzle consisting of three
+-- rods and a number of disks of various diameters which can slide
+-- onto any rod.  Initially, all the disks are stacked in decreasing
+-- size order so that they form a conical shape.  The objective to
+-- move the entire stack to one of the other two rods, with each move
+-- consisting of taking the uppermost disk from one of the rods and
+-- placing it on top of the stack on another one.  A disk cannot be
+-- placed on top of a disk of smaller diameter.
+--
+-- Write a function which generates an optimal solution to the puzzle.
+-- The rods are numbered 1-3, with the stack starting on rod 1.  Your
+-- function should return a list of {from = <rod>, to = <rod>} tables,
+-- and will receive the number of disks in the original stack as its
+-- argument.
+--
+-- Solution --------------------------------------------------------------------
+function towers_of_hanoi_solution(disk_count)
+	-- Your implementation here
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+local function disk_stack(count)
+	local stack = {}
+	for i = count, 1, -1 do table.insert(stack, i) end
+	return stack
+end
+
+local function assert_valid(state)
+	for _, rod in ipairs(state) do
+		local previous = rod[1]
+		for _, disk in ipairs(rod) do
+			luaunit.assertTrue(disk <= previous)
+			previous = disk
+		end
+	end
+	return true
+end
+
+local function assert_solved(state, disk_count)
+	luaunit.assertEquals(state[1], {})
+	if #state[2] ~= 0 then
+		luaunit.assertEquals(state[2], disk_stack(disk_count))
+		luaunit.assertEquals(state[3], {})
+	else
+		luaunit.assertEquals(state[2], {})
+		luaunit.assertEquals(state[3], disk_stack(disk_count))
+	end
+end
+
+local function assert_is_solution(solution, disk_count)
+	local state = {disk_stack(disk_count), {}, {}}
+	for i, move in ipairs(solution) do
+		local disk = table.remove(state[move.from])
+		table.insert(state[move.to], disk)
+		assert_valid(state)
+	end
+	assert_solved(state, disk_count)
+end
+
+local function test_with_count(disk_count)
+	local solution = towers_of_hanoi_solution(disk_count)
+	assert_is_solution(solution, disk_count)
+	luaunit.assertEquals(#solution, 2 ^ disk_count - 1)
+end
+
+function test_with_1_disk()
+	test_with_count(1)
+end
+
+function test_with_7_disks()
+	test_with_count(7)
+end
+
+function test_with_12_disks()
+	test_with_count(12)
+end
+
+os.exit(luaunit.LuaUnit.run())

19_dependencies.lua

@@ -0,0 +1,105 @@
+-- Write a function to generate a valid order for a number of jobs
+-- that depend upon each other.  Your input is a jobs table; each key
+-- is a job number, with its the values being a list jobs it depends
+-- on.  You may assume that there are no circular dependencies.
+--
+-- Return a list of job numbers, so that performing the jobs in that
+-- order ensures that all jobs are exactly once, and all dependencies
+-- of a job are done before prior to it.
+--
+-- Solution --------------------------------------------------------------------
+function schedule(jobs)
+	-- Your implementation here
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+local function keys(t)
+	local results = {}
+	for key, _ in pairs(t) do table.insert(results, key) end
+	return results
+end
+
+local function contains(list, target)
+	for _, item in ipairs(list) do if item == target then return true end end
+	return false
+end
+
+local function deep_copy(original)
+	local copy = {}
+	if type(original) == "table" then
+		for key, value in pairs(original) do
+			local key_copy = deep_copy(key)
+			local value_copy = deep_copy(value)
+			copy[key_copy] = value_copy
+		end
+	else
+		copy = original
+	end
+	return copy
+end
+
+local function assert_valid(order, jobs)
+	local done = {}
+	for _, job in ipairs(order) do
+		for _, dependency in ipairs(jobs[job]) do
+			luaunit.assertTrue(contains(done, dependency))
+		end
+		table.insert(done, job)
+	end
+end
+
+local function test_case(jobs)
+	local order = schedule(deep_copy(jobs))
+	luaunit.assertItemsEquals(order, keys(jobs))
+	assert_valid(order, jobs)
+end
+
+function test_sequential_dependencies()
+	local jobs = {[1] = {2}, [2] = {3}, [3] = {}}
+	test_case(jobs)
+end
+
+function test_converging_dependencies()
+	local jobs = {
+		[1] = {5},
+		[2] = {5},
+		[3] = {6},
+		[4] = {6},
+		[5] = {7},
+		[6] = {7},
+		[7] = {},
+	}
+	test_case(jobs)
+end
+
+function test_diverging_dependencies()
+	local jobs = {
+		[1] = {2, 3},
+		[2] = {4, 5},
+		[3] = {6, 7},
+		[4] = {},
+		[5] = {},
+		[6] = {},
+		[7] = {}
+	}
+	test_case(jobs)
+end
+
+function test_compound_dependencies()
+	local jobs = {
+		[1] = {2, 3, 4},
+		[2] = {5, 6},
+		[3] = {7},
+		[4] = {7},
+		[5] = {},
+		[6] = {8},
+		[7] = {8},
+		[8] = {}
+	}
+	test_case(jobs)
+end
+
+os.exit(luaunit.LuaUnit.run())

20_legal_captures.lua

@@ -0,0 +1,340 @@
+-- Write a function which takes a description of a chess position and
+-- returns a list of all legal captures from that position.
+--
+-- The position will be given as a table, containing the keys "turn",
+-- indicating which player it is to move, "board", which will contain
+-- a rank-major grid of pieces (that is, a list of ranks/rows).  Each
+-- piece will be indicated by its unicode symbol.  The lack of a piece
+-- will be indicated by nil.  If the previous move was a pawn moving
+-- two places, the key "en_passant_target" will be set to a table with
+-- "rank" and "file" keys set to the (1-based) rank and file indices
+-- of the square passed over by the pawn.
+--
+-- For example, the starting position would be given as:
+--
+-- {
+--     turn = "white",
+--     board = {
+--         {"♖", "♘", "♗", "♕", "♔", "♗", "♘", "♖"},
+--         {"♙", "♙", "♙", "♙", "♙", "♙", "♙", "♙"},
+--         {nil, nil, nil, nil, nil, nil, nil, nil},
+--         {nil, nil, nil, nil, nil, nil, nil, nil},
+--         {nil, nil, nil, nil, nil, nil, nil, nil},
+--         {nil, nil, nil, nil, nil, nil, nil, nil},
+--         {"♟︎", "♟︎", "♟︎", "♟︎", "♟︎", "♟︎", "♟︎", "♟︎"},
+--         {"♜", "♞", "♝", "♛", "♚", "♝", "♞", "♜"},
+--     },
+-- }
+--
+-- Moves should be returned in figurine algebraic notation, without
+-- indicators for en passant, check or checkmate (i.e. no "e.p.", "+"
+-- or "#").  For example, "♞xc6" for a black night capturing on c6 and
+-- "exd7" for an e-file pawn capturing on d7.  For the sake of
+-- simplicity, there's no requirement to disambiguate between two
+-- pieces of the same type when the notation for the capture would
+-- otherwise be the same (e.g. if two rooks can capture on the same
+-- square).  However, there should be duplicate entries in the results
+-- list for each.
+--
+-- Solution --------------------------------------------------------------------
+function legal_captures(position)
+	-- Your implementation here
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luaunit")
+
+function test_starting_position()
+	local position = {
+		turn = "white",
+		board = {
+			{"♖", "♘", "♗", "♕", "♔", "♗", "♘", "♖"},
+			{"♙", "♙", "♙", "♙", "♙", "♙", "♙", "♙"},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{"♟︎", "♟︎", "♟︎", "♟︎", "♟︎", "♟︎", "♟︎", "♟︎"},
+			{"♜", "♞", "♝", "♛", "♚", "♝", "♞", "♜"},
+		},
+	}
+	local expected = {}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_queens_gambit()
+	local position = {
+		turn = "black",
+		board = {
+			{"♖", "♘", "♗", "♕", "♔", "♗", "♘", "♖"},
+			{"♙", "♙", nil, nil, "♙", "♙", "♙", "♙"},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, "♙", "♙", nil, nil, nil, nil},
+			{nil, nil, nil, "♟︎", nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{"♟︎", "♟︎", "♟︎", nil, "♟︎", "♟︎", "♟︎", "♟︎"},
+			{"♜", "♞", "♝", "♛", "♚", "♝", "♞", "♜"},
+		},
+	}
+	local expected = {"dxc4"}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_scandinavian_defense()
+	local position = {
+		turn = "white",
+		board = {
+			{"♖", "♘", "♗", "♕", "♔", "♗", "♘", "♖"},
+			{"♙", "♙", "♙", "♙", nil, "♙", "♙", "♙"},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, "♙", nil, nil, nil},
+			{nil, nil, nil, "♟︎", nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{"♟︎", "♟︎", "♟︎", nil, "♟︎", "♟︎", "♟︎", "♟︎"},
+			{"♜", "♞", "♝", "♛", "♚", "♝", "♞", "♜"},
+		},
+	}
+	local expected = {"exd5"}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_knight_captures()
+	local position = {
+		turn = "black",
+		board = {
+			{"♙", "♙", "♙", "♙", "♙", "♙", "♙", "♙"},
+			{"♙", "♙", "♙", nil, "♙", "♙", "♙", "♙"},
+			{"♙", "♙", nil, nil, nil, "♙", "♙", "♙"},
+			{"♙", nil, nil, "♞", nil, nil, "♙", "♙"},
+			{"♙", "♙", nil, nil, nil, "♙", "♙", "♙"},
+			{"♙", "♙", "♙", nil, "♙", "♙", "♙", "♙"},
+			{"♙", "♙", "♙", "♙", "♙", "♙", "♙", "♙"},
+			{"♙", "♙", "♙", "♙", "♙", "♙", "♙", "♙"},
+		},
+	}
+	local expected = {
+		"♞xb3", "♞xb5", "♞xc2", "♞xc6", "♞xe2", "♞xe6", "♞xf3", "♞xf5",
+	}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_knight_not_blocked()
+	local position = {
+		turn = "white",
+		board = {
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, "♟︎", "♟︎", "♟︎", nil, nil},
+			{nil, nil, nil, nil, "♟︎", nil, nil, nil},
+			{nil, nil, "♟︎", "♟︎", "♘", nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+		},
+	}
+	local expected = {"♘xd3", "♘xf3"}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_bishop_captures()
+	local position = {
+		turn = "black",
+		board = {
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{"♙", nil, nil, nil, nil, nil, "♙", nil},
+			{nil, nil, nil, "♙", nil, nil, "♙", nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, "♙", "♝", nil, nil, nil, "♙"},
+			{nil, nil, nil, nil, "♙", nil, nil, nil},
+			{nil, "♙", nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, "♙", nil, nil, nil, nil},
+		},
+	}
+	local expected = {"♝xa2", "♝xb7", "♝xe6", "♝xg2"}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_bishop_blocked()
+	local position = {
+		turn = "black",
+		board = {
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, "♙", nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, "♞", nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, "♝", nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+		},
+	}
+	local expected = {}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_rook_captures()
+	local position = {
+		turn = "white",
+		board = {
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{"♟︎", nil, nil, nil, nil, nil, "♟︎", nil},
+			{nil, nil, nil, "♟︎", nil, nil, "♟︎", nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, "♟︎", "♖", nil, nil, nil, "♟︎"},
+			{nil, nil, nil, nil, "♟︎", nil, nil, nil},
+			{nil, "♟︎", nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, "♟︎", nil, nil, nil, nil},
+		},
+	}
+	local expected = {"♖xc5", "♖xd3", "♖xd8", "♖xh5"}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_rook_blocked()
+	local position = {
+		turn = "white",
+		board = {
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, "♖", "♙", nil, nil, nil, "♟︎", nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+		},
+	}
+	local expected = {}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_queen_captures()
+	local position = {
+		turn = "black",
+		board = {
+			{nil, "♙", "♙", "♙", "♙", "♙", nil, "♙"},
+			{"♙", "♙", "♙", nil, "♙", "♙", "♙", "♙"},
+			{"♙", "♙", nil, nil, nil, "♙", "♙", "♙"},
+			{"♙", nil, nil, "♛", nil, nil, "♙", nil},
+			{"♙", "♙", nil, nil, nil, "♙", "♙", "♙"},
+			{"♙", "♙", "♙", nil, "♙", "♙", "♙", "♙"},
+			{nil, "♙", "♙", "♙", "♙", "♙", nil, "♙"},
+			{"♙", "♙", "♙", nil, "♙", "♙", "♙", nil},
+		},
+	}
+	local expected = {
+		"♛xa4", "♛xb2", "♛xb6", "♛xd1", "♛xd7", "♛xf2", "♛xf6", "♛xg4",
+	}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_queen_blocked()
+	local position = {
+		turn = "white",
+		board = {
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, "♟︎", nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, "♙", nil, nil, nil, nil, nil},
+			{nil, "♕", "♙", nil, nil, nil, "♟︎", nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+		},
+	}
+	local expected = {}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_king_captures()
+	local position = {
+		turn = "black",
+		board = {
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, "♙", "♙", "♙", nil, nil, nil},
+			{nil, nil, "♙", "♚", "♙", nil, nil, nil},
+			{nil, nil, "♙", "♙", "♙", nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+		},
+	}
+	local expected = {"♚xc3","♚xc4","♚xc5","♚xd3","♚xd5","♚xe3","♚xe4","♚xe5",}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_en_passant()
+	local position = {
+		turn = "white",
+		board = {
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, "♟︎", "♙", nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+		},
+		en_passant_target = {rank = 6, file = 4},
+	}
+	local expected = {"exd6"}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_cannot_capture_if_leads_to_check()
+	local position = {
+		turn = "white",
+		board = {
+			{nil, nil, nil, nil, "♔", nil, nil, nil},
+			{nil, nil, nil, nil, "♗", nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, "♟︎", nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, "♜", nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+		},
+		en_passant_target = {rank = 6, file = 4},
+	}
+	local expected = {}
+	luaunit.assertItemsEquals(legal_captures(position), expected)
+end
+
+function test_position_with_lots_of_captures()
+	local position = {
+		turn = "white",
+		board = {
+			{"♚", nil, nil, "♔", "♝", nil, nil, "♖"},
+			{nil, "♖", "♜", "♕", "♞", "♕", "♘", nil},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{"♗", "♛", "♕", "♝", "♕", "♛", "♕", "♞"},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, "♕", "♝", "♕", "♛", "♕", "♘", "♗"},
+			{nil, nil, nil, nil, nil, nil, nil, nil},
+			{nil, nil, nil, "♜", "♕", "♛", nil, nil},
+		},
+		en_passant_target = {rank = 6, file = 4},
+	}
+	local expected = {
+		"♔xe1", "♔xe2", "♔xc2", "♖xh4", "♖xe1",
+		"♖xb4", "♖xc2", "♕xf4", "♕xb4", "♕xe1",
+		"♕xd4", "♕xe2", "♕xc2", "♕xh4", "♕xd4",
+		"♕xe1", "♕xf4", "♕xe2", "♘xh4", "♘xf4",
+		"♘xe1", "♗xc6", "♗xc2", "♕xe6", "♕xe2",
+		"♕xc6", "♕xc2", "♕xd4", "♕xb4", "♕xc6",
+		"♕xc2", "♕xe6", "♕xe2", "♕xf4", "♕xd4",
+		"♕xe6", "♕xe2", "♕xh4", "♕xf4", "♕xd8",
+		"♕xd4", "♕xb4", "♕xc6", "♕xf8", "♕xf4",
+		"♕xb4", "♕xd8", "♕xd4", "♕xe6", "♕xc6",
+		"♕xd8", "♕xh4", "♕xd4", "♕xf8", "♕xf4",
+		"♕xe6", "♘xf8", "♘xh4", "♘xf4", "♗xf8",
+		"♗xf4", "♕xc6", "♕xe6", "♕xf8", "♕xd8",
+	}
+	local captures = legal_captures(position)
+	luaunit.assertItemsEquals(captures, expected)
+end
+
+os.exit(luaunit.LuaUnit.run())

README.md

@@ -0,0 +1,39 @@
+# Lua Exercises
+
+This repo contains some Lua exercises along with automated tests for
+solutions.  Each file contains a description of the problem and an
+area for a solution as well as the tests.
+
+## Set Up
+
+To get started, create a fork of this repo on your own account (with
+the "Fork" button in the top-left of the Gitea page"), then clone it,
+passing the `--recursive` flag.  If you already cloned it without
+passing `--recursive`, you can run `git submodule update --init` to
+fix it.
+
+```sh
+git clone --recursive git@git.wip.sh:<your-username>/lua-exercises.git
+```
+
+## Doing the Exercises
+
+It's recommended that you roughly stick to the defined order of the
+exercises, but feel free to deviate if you wish.  Some of the
+exercises are relatively easy, whereas some of them (especially the
+last few) are quite challenging; do not be disheartened if solving a
+particular exercise takes you a long time, and feel free to ask for
+help in the Discord server if you feel you are stuck.
+
+You can define as many functions and constants as you need in the
+solution area.  You might find it useful to temporarily comment out
+some of the tests to work through the cases one by one (especially on
+the more complex exercises), but do not modify the test code other
+than this, and make sure all the cases are un-commented again before
+considering the exercise solved.
+
+To run the tests and check your solution for a given exercise, simply
+run `lua <the-file>`.  For example, if you were working on the
+anagrams exercise, you would run `lua 08_anagrams.lua`.  For each
+exercise, the tests should run in well under a tenth of a second; if
+it takes longer than this you should try to speed up your solution.