535. Encode and Decode TinyURL

Problem

Note: This is a companion problem to the System Design problem: Design TinyURL.

TinyURL is a URL shortening service where you enter a URL such as https://leetcode.com/problems/design-tinyurl and it returns a short URL such as http://tinyurl.com/4e9iAk. 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 given longUrl.

• String decode(String shortUrl) Returns the original long URL for the given shortUrl. It is guaranteed that the given shortUrl was 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 deconding it.

  Constraints:

• 1 <= url.length <= 10^4

• url is guranteed to be a valid URL.

Solution (Java)

public class Codec {
    private Map<String, String> map = new HashMap<>();
    private int n = 0;

    // Encodes a URL to a shortened URL.
    public String encode(String longUrl) {
        n++;
        String ans = "http://tinyurl.com/";
        ans += Integer.toString(n);
        map.put(ans, longUrl);
        return ans;
    }

    // Decodes a shortened URL to its original URL.
    public String decode(String shortUrl) {
        return map.get(shortUrl);
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.decode(codec.encode(url));

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).