URL Shortener: Counter vs Hash

Problem

Create a URL shortener.

Input: long URL
Output: short URL

Details

Two main problems:

1. How to generate a short code
2. Handle collision (if applicable)

Two Approaches

1. Counter + Base62 encoding: No collisions
2. Hash + Collision Handling

Approach 1: Counter + Base62 encoding

Table: urls

- id (primary key, auto-increment)
- long_url (text, not null)
- short_url (varchar(100), not null)
- created_at (timestamp)

Algorithm

1. Check if long_url exists in DB
   • If yes, return existing short_url
   • If no, continue
2. Get row count → increment by 1 → base62 encode
3. Insert (long_url, short_url) into table
4. Return short_url

Result: There is no chance of collision here.

Code: encoding.py

Approach 2: Hash + Collision Resolution

Algorithm

1. Hash long_url with md5 → take first 7 chars
2. Check if hash exists in DB:
   • Exists + same URL → duplicate → return existing
   • Exists + different URL → collision → append counter (or re-hash with salt) until empty slot is found
   • Doesn't exist → insert directly
3. Return short_url

Code: hashing.py

When to Use