Encode and Decode TinyURL
Last Updated: November 15, 2025
Problem Description
TinyURL is a URL shortening service where you enter a URL such as and it returns a short URL such as . Design a class to encode a URL and decode a tiny URL.
There is no restriction on how your encode/decode algorithm should work. You just need to ensure that a URL can be encoded to a tiny URL and the tiny URL can be decoded to the original URL.
Implement the Solution class:
Solution()Initializes the object of the system.String encode(String longUrl)Returns a tiny URL for the givenlongUrl.String decode(String shortUrl)Returns the original long URL for the givenshortUrl. It is guaranteed that the givenshortUrlwas encoded by the same object.
Example 1:
Input: url = "https://leetcode.com/problems/design-tinyurl"
Output: "https://leetcode.com/problems/design-tinyurl"Explanation:
Solution obj = new Solution();
string tiny = obj.encode(url); // returns the encoded tiny url.
string ans = obj.decode(tiny); // returns the original url after decoding it.
Constraints:
- 1 <= url.length <= 104
urlis guranteed to be a valid URL.
Solve it on LeetCode
Approaches
1. HashMap with Simple Incremental ID
Intuition:
The basic idea is to use a simple Integer counter to assign a unique ID to each URL. We maintain a mapping of the ID to the original URL using a HashMap. The ID is then converted to a string and appended to our base URL (e.g., http://tinyurl.com/).
Steps:
- Use a HashMap to store the mapping between an ID and the original URL.
- Maintain an Integer counter that increments with each new URL.
- To encode a URL, map it with the current counter value and increment the counter.
- To decode, simply retrieve the URL from the HashMap using the ID.
Code:
- Time Complexity: O(1) for both
encodeanddecodemethods. - Space Complexity: O(N), where N is the number of URLs encoded. We store each URL once.
2. HashMap with Random and Base62 Encoding
Intuition:
To improve collision handling and reduce the size of the keys, we use random strings as keys. Base62 encoding is employed for key generation, consisting of alphanumeric characters (a-z, A-Z, 0-9), allowing for a wide range of unique combinations.
Steps:
- Use a HashMap to map between encoded keys and URLs.
- Generate a unique key for each URL using random strings.
- Use Base62 encoding to ensure a consistent string length and avoid collisions.
- To encode, generate a key, map it to the URL, and build the tiny URL.
- To decode, retrieve the URL directly using the key.
Code:
- Time Complexity: O(1) for both
encodeanddecodemethods, on average. - Space Complexity: O(N), where N is the number of URLs encoded. We store each URL once.