Encode and Decode Strings

https://leetcode.com/problems/encode-and-decode-strings

Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and is decoded back to the original list of strings.

Machine 1 (sender) has the function:

string encode(vector strs) { // ... your code return encoded_string; } Machine 2 (receiver) has the function: vector decode(string s) { //... your code return strs; } So Machine 1 does:

string encoded_string = encode(strs); and Machine 2 does:

vector strs2 = decode(encoded_string); strs2 in Machine 2 should be the same as strs in Machine 1.

Implement the encode and decode methods.

You are not allowed to solve the problem using any serialize methods (such as eval).

Example 1:

Input: dummy_input = ["Hello","World"]
Output: ["Hello","World"]
Explanation:
Machine 1:
Codec encoder = new Codec();
String msg = encoder.encode(strs);
Machine 1 ---msg---> Machine 2

Machine 2:
Codec decoder = new Codec();
String[] strs = decoder.decode(msg);
Example 2:

Input: dummy_input = [""]
Output: [""]
 

Constraints:

1. 1 <= strs.length <= 200
2. 0 <= strs[i].length <= 200
3. strs[i] contains any possible characters out of 256 valid ASCII characters.

Follow up: Could you write a generalized algorithm to work on any possible set of characters?

Implementation :

public class Codec {

    // Encodes a list of strings to a single string.
    public String encode(List<String> strs) {
        if (strs == null || strs.size() < 1)
        return "";
        String separator = "#";
        String encodedString = "";
        int n = strs.size();
        for (int i = 0; i < n; i++) {
            String str = strs.get(i);
            String code = str.length() + separator + str;
            encodedString = encodedString + code;
        }
        return encodedString;
    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String str) {
        List<String> strs = new ArrayList<>();
        if(str.length() == 0)
            return strs;
        int index = 0;
        while (index < str.length()) {
            String decodedString = "";
            String len = "";
            while(str.charAt(index) != '#') {
                len = len + str.charAt(index);
                index++;
            }
            index++;
            int stringLength = Integer.parseInt(len);
            if(stringLength != 0) {
                decodedString = str.substring(index, index + stringLength);
                index = index + stringLength;
            }
            strs.add(decodedString);
        }
      return strs;
   }
}

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

References :

https://www.youtube.com/shorts/NgalRGKmErU