If there is a long url, I want to generate a short URL like those in Twitter. Is there some way to implement this in Ruby?
The easiest way is to:
Encoding to base 36/decoding from base 36 is simple in Ruby:
12341235.to_s(36)
#=> "7cik3"
"7cik3".to_i(36)
#=> 12341235
Encoding to base 62 is a bit tricker. Here's one way to do it:
module AnyBase
ENCODER = Hash.new do |h,k|
h[k] = Hash[ k.chars.map.with_index.to_a.map(&:reverse) ]
end
DECODER = Hash.new do |h,k|
h[k] = Hash[ k.chars.map.with_index.to_a ]
end
def self.encode( value, keys )
ring = ENCODER[keys]
base = keys.length
result = []
until value == 0
result << ring[ value % base ]
value /= base
end
result.reverse.join
end
def self.decode( string, keys )
ring = DECODER[keys]
base = keys.length
string.reverse.chars.with_index.inject(0) do |sum,(char,i)|
sum + ring[char] * base**i
end
end
end
...and here it is in action:
base36 = "0123456789abcdefghijklmnopqrstuvwxyz"
db_id = 12341235
p AnyBase.encode( db_id, base36 )
#=> "7cik3"
p AnyBase.decode( "7cik3", base36 )
#=> 12341235
base62 = [ *0..9, *'a'..'z', *'A'..'Z' ].join
p AnyBase.encode( db_id, base62 )
#=> "PMwb"
p AnyBase.decode( "PMwb", base62 )
#=> 12341235
Edit
If you want to avoid URLs that happen to be English words (for example, four-letter swear words) you can use a set of characters that does not include vowels:
base31 = ([*0..9,*'a'..'z'] - %w[a e i o u]).join
base52 = ([*0..9,*'a'..'z',*'A'..'Z'] - %w[a e i o u A E I O U]).join
However, with this you still have problems like AnyBase.encode(328059,base31)
or AnyBase.encode(345055,base31)
or AnyBase.encode(450324,base31)
. You may thus want to avoid vowel-like numbers as well:
base28 = ([*'0'..'9',*'a'..'z'] - %w[a e i o u 0 1 3]).join
base49 = ([*'0'..'9',*'a'..'z',*'A'..'Z'] - %w[a e i o u A E I O U 0 1 3]).join
This will also avoid the problem of "Is that a 0 or an O?" and "Is that a 1 or an I?".