Create postfix exercise

13_prime_sieve.lua

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+-- 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_run_length_encoding.lua

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+-- 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())

15_postfix.lua

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+-- 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())