Decimal number to Roman numeral

Number to Roman numeral converter

The Roman empire had one of the greates armies in history. It was big, and large, and vast. In fact, it was so big that only one person in the whole Empire could count that high. The problem was that he learned counting in the Sofia Math Highshcool, where only Arabic numbers were taught. So every time the Emperor asked “How big is our army?” the reply was meaningless to him.

Help him by writing a method number_to_roman that converts from an Arabic number to a roman literal. Also, keep it as short as possible as the Emperor is quite slow with the keyboard and the Empire might fall before he’s finished typing it in.

Examples:

number_to_roman(1)    => 'I'
number_to_roman(13)   => 'XIII'
number_to_roman(2016) => 'MMXVI'

Leader board

The lower the score - the better. It is the shortest solution that wins.

If you're among the first 5 stop by out booth to claim your reward.

Winner!

Nickname: Rosa
   Score: 120

def number_to_roman(n)
  %w(M CM D CD C XC L XL X IX V IV I).zip(%w(1000 900 500 400 100 90 50 40 10 9 5 4 1)).map{ |l,v|
    a, n=n.divmod v.to_i
    l*a
  }*''
end

Winner!

Nickname: janosch-jo
   Score: 125

def number_to_roman n
  'M1000CM900D500CD400C100XC90L50XL40X10IX9V5IV4I1'
  .scan(/(\D+)(\d+)/)
  .map { |k, v|
    c, n = n.divmod v.to_i
    k*c
  } * ''
end

Winner!

Nickname: babi
   Score: 136

def number_to_roman(n)
  {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}.map{|l,v|a,n=n.divmod v;l.to_s*a}.join
end

Winner!

Nickname: timrogers
   Score: 138

R = {
  M: 1e3,
  CM: 900,
  D: 500,
  CD: 400,
  C: 100,
  XC: 90,
  L: 50,
  XL: 40,
  X: 10,
  IX: 9,
  V: 5,
  IV: 4,
  I: 1
}

def number_to_roman i
  R.map{|(l,n)|q,r = i.divmod n
    i = r
    "#{l}"*q
  }*""
end

Winner!

Nickname: Joskov
   Score: 145

def f n
  o = [1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000]
  i = (o.find_index { |x| x > n } || 0) - 1
  n > 0 ? %w(I IV V IX X XL L XC C CD D CM M)[i] + f(n - o[i]) : ''
end
alias number_to_roman f

Nickname: ben_
   Score: 151

def number_to_roman(number)
  {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}.map{|l,v|a,number=number.divmod v;l.to_s*a}.join
end

Nickname: J-_-L
   Score: 157

def number_to_roman n
s=""
%w[M C X I].zip([n/1000,n/100,n/10,n]){|l,m|s+=l.*m%10}
[%w[I V X],%w[X L C],%w[C D M]].map{|a,b,c|s.gsub!a*9,a+c
s.gsub!a*5,b
s.gsub!a*4,a+b}
s
end

Nickname: fp
   Score: 160

def number_to_roman(n)
  r = %w[1000 900 500 400 100 90 50 40 10 9 5 4 1].map(&:to_i).zip(%w[M CM D CD C XC L XL X IX V IV I])
  z = ""
  while n > 0 && r.any?
    k, v = r.first
    n - k >= 0 ? (z << v; n -= k) : r.shift
  end
  z
end

Nickname: Luca
   Score: 162

def number_to_roman n,a=""
  n==0 ? a : (
  k,v=([1000]+[100,10,1].flat_map{|x|
     [9,5,4,1].map{|y| x*y}
   }).zip(%w[M CM D CD C XC L XL X IX V IV I]).find {|k| k[0]<=n}
   number_to_roman n-k, a+v)
end

Nickname: Luke
   Score: 165

def number_to_roman(n,a="")
  n==0 ? a : (
  k,v=([1000]+[100,10,1].flat_map{|x|
     [9,5,4,1].map{|y| x*y}
   }).zip(%w[M CM D CD C XC L XL X IX V IV I]).find {|k, v| k<=n}
   number_to_roman(n-k, a+v))
end

Nickname: Lucaong
   Score: 169

def number_to_roman(n,a="")
  return a if n==0
  k,v=([1000]+[100,10,1].flat_map{|x|
     [9,5,4,1].map{|y| x*y}
   }).zip(%w[M CM D CD C XC L XL X IX V IV I]).find {|k,v| k<=n}
  number_to_roman(n-k, a+v)
end

Nickname: Joan
   Score: 174

def number_to_roman(x)
[3,2,1,0].map{|i|n=x.to_s.rjust(4,'0')[3-i].to_i;g=%w(I V X L C D M _ _).slice(i*2,i*2+3);n>=0&&n<4?g[0]*n: n==4?g[0]+g[1]: n==9?g[0]+g[2]:g[1]+g[0]*(n-5)}.join
end

Nickname: tpavel
   Score: 200

C = [
  ['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]
]

def number_to_roman(n)
  r = ''

  C.each do |s|
    while n >= s[1]
      r += s[0]
      n -= s[1]
    end
  end

  r
end

Nickname: Ben
   Score: 201

def number_to_roman(number)
  { "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 }.map do |ltr, val| 
    amt, number = number.divmod(val)
    ltr * amt
  end.join
end

Nickname: M. Valenzuela
   Score: 218

def number_to_roman(number)
  ''.tap do |r|
    m={1000=>'M',900=>'CM',500=>'D',400=>'CD',100=>'C',90=>'XC',50=>'L',40=>'XL',10=>'X',9=>'IX',5=>'V',4=>'IV',1=>'I'}
    while(number!=0) do
      k,v=m.find{|k,_|k<=number}
      number-=k
      r<<v
    end
  end
end

Nickname: xijo
   Score: 237

def number_to_roman(n)
  h = {
    M:1000,
    D:500,
    C:100,
    L:50,
    X:10,
    V:5,
    I:1
  }
  s = h.map{ |k, v|
    c, n = n.divmod(v)
    k.to_s*c
  } * ''

  h.keys.each_with_index { |k, i|
    before = h.keys[i-1]
    s.sub!(/#{before}#{k}{4}/, "#{k}#{h.keys[i-2]}")
    s.sub!(/#{k}{4}/, "#{k}#{h.keys[i-1]}")
  }
  s
end