discard """
file: "tromans.nim"
output: "success"
"""
import
strutils
## Convert an integer to a Roman numeral
# See http://en.wikipedia.org/wiki/Roman_numerals for reference
proc raiseInvalidValue(msg: string) {.noreturn.} =
# Yes, we really need a shorthand for this code...
var e: ref EInvalidValue
new(e)
e.msg = msg
raise e
# I should use a class, perhaps.
# --> No. Why introduce additional state into such a simple and nice
# interface? State is evil. :D
proc RomanToDecimal(romanVal: string): int =
result = 0
var prevVal = 0
for i in countdown(romanVal.len - 1, 0):
var val = 0
case romanVal[i]
of 'I', 'i': val = 1
of 'V', 'v': val = 5
of 'X', 'x': val = 10
of 'L', 'l': val = 50
of 'C', 'c': val = 100
of 'D', 'd': val = 500
of 'M', 'm': val = 1000
else: raiseInvalidValue("Incorrect character in roman numeral! (" &
$romanVal[i] & ")")
if val >= prevVal:
inc(result, val)
else:
dec(result, val)
prevVal = val
proc DecimalToRoman(decValParam: int): string =
# Apparently numbers cannot be above 4000
# Well, they can be (using overbar or parenthesis notation)
# but I see little interest (beside coding challenge) in coding them as
# we rarely use huge Roman numeral.
const romanComposites = [
("M", 1000), ("CM", 900),
("D", 500), ("CD", 400), ("C", 100),
("XC", 90), ("L", 50), ("XL", 40), ("X", 10), ("IX", 9),
("V", 5), ("IV", 4), ("I", 1)]
if decValParam < 1 or decValParam > 3999:
raiseInvalidValue("number not representable")
result = ""
var decVal = decValParam
for key, val in items(romanComposites):
while decVal >= val:
dec(decVal, val)
result.add(key)
for i in 1..100:
if RomanToDecimal(DecimalToRoman(i)) != i: quit "BUG"
for i in items([1238, 1777, 3830, 2401, 379, 33, 940, 3973]):
if RomanToDecimal(DecimalToRoman(i)) != i: quit "BUG"
echo "success" #OUT success