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    <p>The easiest way is to:</p> <ol> <li>keep a database of all URLs</li> <li>when you insert a new URL into the database, find out the id of the auto-incrementing integer primary key.</li> <li>encode that integer into base 36 or 62 (digits + lowercase alpha or digits + mixed-case alpha). Voila! You have a short url!</li> </ol> <p>Encoding to base 36/decoding from base 36 is simple in Ruby:</p> <pre><code>12341235.to_s(36) #=&gt; "7cik3" "7cik3".to_i(36) #=&gt; 12341235 </code></pre> <p>Encoding to base 62 is a bit tricker. Here's one way to do it:</p> <pre><code>module AnyBase ENCODER = Hash.new do |h,k| h[k] = Hash[ k.chars.map.with_index.to_a.map(&amp;: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 &lt;&lt; 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 </code></pre> <p>...and here it is in action:</p> <pre><code>base36 = "0123456789abcdefghijklmnopqrstuvwxyz" db_id = 12341235 p AnyBase.encode( db_id, base36 ) #=&gt; "7cik3" p AnyBase.decode( "7cik3", base36 ) #=&gt; 12341235 base62 = [ *0..9, *'a'..'z', *'A'..'Z' ].join p AnyBase.encode( db_id, base62 ) #=&gt; "PMwb" p AnyBase.decode( "PMwb", base62 ) #=&gt; 12341235 </code></pre> <p><strong>Edit</strong></p> <p>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:</p> <pre><code>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 </code></pre> <p>However, with this you still have problems like <code>AnyBase.encode(328059,base31)</code> or <code>AnyBase.encode(345055,base31)</code> or <code>AnyBase.encode(450324,base31)</code>. You may thus want to avoid vowel-like numbers as well:</p> <pre><code>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 </code></pre> <p><em>This will also avoid the problem of "Is that a 0 or an O?" and "Is that a 1 or an I?".</em></p>
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    1. POhow to implement a short url like urls in twitter?
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    1. POhow to implement a short url like urls in twitter?
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    1. COyou have helped me for many times, i really appreciate your help, the answer every time you offer is great, thank you very very much.
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    2. COBe careful with this implementation, as it will generate human readable words that you might want to avoid. E.g. 645860.to_s(36) = 'duck'. 739172 might be considered a little worse. I recommend to go with base20 (0-9a-j) or similar. To help to decide, you can even use an anagram finder like 'wordplay' like so: `wordplay 'aaabbbcccdddeeefffggghhhiiijjj'` - it shows you which words can be generated.
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    3. CO@user569825 Thanks for the note (though this seems like a poor reason to downvote). I'd suggest perhaps a base set of characters without any vowels as a simpler and less-impactful way.
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