14_vigenere.lua

@@ -1,64 +0,0 @@
--- 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())