I am going to explain one of the common approaches used to create URL shortner.
- Think of an alphabet we want to use. In your case that’s
[a-zA-Z0-9]
. It contains 62 letters. - Take an auto-generated, unique numerical key (the auto-incremented
id
of a MySQL table for example).For this example I will use 12510 (125 with a base of 10).
- Now you have to convert 12510 to X62 (base 62).
12510 = 2×621 + 1×620 =
[2,1]
Now map the indices 2 and 1 to your alphabet. This is how your mapping (with an array for example) could look like:
0 → a 1 → b ... 25 → z ... 52 → 0 61 → 9
With 2 → c and 1 → b you will receive cb62 as the shortened URL.
http://shor.ty/cb
How to resolve a shortened URL to the initial ID
The reverse is even easier. You just do a reverse lookup in your alphabet.
- e9a62 will be resolved to “4th, 61st, and 0th letter in alphabet”.
e9a62 =
[4,61,0]
= 4×622 + 61×621 + 0×620 = 1915810 - Now find your database-record with
WHERE id = 19158
and do the redirect.