Add readme describing repo and how to run tests

.template.lua

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

README.md

@@ -0,0 +1,13 @@
+# Lua Exercises
+
+This repo contains some Lua exercises along with automated tests for
+their solutions.  Each file contains a description of the problem and
+an area for your solution as well as the tests.  Feel free to define
+as many functions and constants as you need in the solution area, but
+do not modify the tests.
+
+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 xxx_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.

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

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

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

greatest_common_divisor.lua

@@ -1,3 +1,7 @@
+-- The greatest common divisor (GCD) of two numbers X and Y is, as the
+-- name suggests, the largest number which evenly divides both X and
+-- Y.  Implement the function below to calculate this.
+--
 -- Solution --------------------------------------------------------------------
 function greatest_common_divisor(x, y)
 	-- Your implementation here

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

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

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

maximum.lua

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

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

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

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

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