In CSS, colours can be specified by a "hex triplet" - a three byte (six digit) hexadecimal number where each byte represents the red, green, or blue components of the colour. For instance, #FF0000 is completely red, and is equivalent to rgb(255, 0, 0).

Colours can also be represented by the shorthand notation which uses three hexadecimal digits. The shorthand expands to the six digit form by duplicating each digit. For instance, #ABC becomes #AABBCC.

Since there are fewer digits in the hex shorthand, fewer colours can be represented.

The challenge

Write a program or function that takes a six digit hexadecimal colour code and outputs the closest three-digit colour code.

Here's an example:

• Input hex code: #28a086


• Red component
  
  
  • 0x28 = 40 (decimal)
  
  
  • 0x22 = 30
  
  
  • 0x33 = 51
  
  
  • 0x22 is closer, so the first digit of the shortened colour code is 2
  
  


• Green component
  
  
  • 0xa0 = 160
  
  
  • 0x99 = 153
  
  
  • 0xaa = 170
  
  
  • 0x99 is closer, so the second digit is 9
  
  


• Blue component
  
  
  • 0x86 = 134
  
  
  • 0x77 = 119
  
  
  • 0x88 = 136
  
  
  • 0x88 is closer, so the third digit is 8
  
  


• The shortened colour code is #298 (which expands to #229988)

Your program or function must accept as input a six digit hexadecimal colour code prepended with # and output a three digit colour code prepended with #.

Examples

• #FF0000 → #F00


• #00FF00 → #0F0


• #D913C4 → #D1C


• #C0DD39 → #BD3


• #28A086 → #298


• #C0CF6F → #BC7

Scoring

This is a code-golf challenge, so shortest answer in your language wins! Standard rules apply.

Japt, 16 bytes

r"%w"²_n16_r17Ãg

Try it or run all test cases

r"%w"²_n16_r17Ãg :Implicit input of string
r :Replace
 "%w" :RegEx /w/g
 ² :Duplicate, giving /ww/g
 _ :Pass each match through a function
 n16 : Convert to decimal
 _ : Pass through the following function, and convert back to hex
 r17 : Round to the nearest multiple of 17
 Ã : End function
 g : Get first character

Python 3, 72 70 68 bytes

lambda x:'#'+''.join(f"(int(x[i:i+2],16)+8)//17:X"for i in(1,3,5))

Try it online!

This is a port of Grzegorz Oledzkis original answer, which I helped him golfing down.

Two features of Python 3 help us save bytes:

• Floating point division by default


• Format string literals

-2 bytes thanx to Jonathan Allan

JavaScript (ES6), 55 bytes

s=>s.replace(/w./g,x=>(('0x'+x)/17+.5|0).toString(16))

Try it online!

Python 2 (109 101 97 85 83 74 bytes)

lambda x:'#'+''.join(hex(int(int(x[i:i+2],16)/17.+.5))[2:]for i in[1,3,5])

The "nearest distance" is handled by division by 17 and rounding.

Improvements:

-8 bytes by using the int(...+.5) trick instead of int(round(...))

-4 bytes by using list comprehension instead of map()

-1 byte by hardcoding # in the output (thanks @movatica)

-10 bytes by not using re.findall("..",...) in favor of explicit String splicing

-2 bytes by not using list comprehension, but an inline generator expression in join (thanks @movatica)

-1 byte by not splicing the :7 ending for blue part

-9 bytes by better iteration over colors - i.e. iterating over indices, not actual characters (thanks @movatica)