Dictionary Encoding Java

Dictionary encoding is a loss-less compression technique to compress a list of words. Dictionary encoding works by maintaining a mapping of unique words to their compressed value, and replacing occurrence of the words with the compressed value

Here is an example:

Input String:
“USA,USA,USA,USA,Mexico,Canada,Mexico,Mexico,Mexico,Argentina”

Potential Encoder Output String:
“USA,Mexico,Canada,Argentina:0,0,0,0,1,2,1,1,1,3”

The code is assigned to the country in the order they appear in the input, starting from 0 and so on

decode(encode(input)) = input

Solution:

class Solution
{
 public static String encode(final String input) {
 
 // Split the input string to assist encoding
    String[] encoded = input.split(",");
    int n = encoded.length;
// Map to store the country and it's encoding
    Map<String, Integer> encoding = new HashMap<>();
    // Map for unique countries to provide a reverse lookup for encoding
    Map<Integer, String> uniqueCountries = new HashMap<>();
    int counter = 0;
// create a map for country and it's code
    for( int i=0; i<n; i++) {
      if(encoding.containsKey(encoded[i])) {
        continue;
      }
      
      encoding.put(encoded[i], counter);
      uniqueCountries.put(counter, encoded[i]);
      counter++;
    }
StringBuilder sb = new StringBuilder();
int i=0, j=0;
// encode the map using the reverse look up of the country code
 // You can also use a map that maintains the input order instead of
 // reverse lookup
    for(Map.Entry<Integer, String> x: uniqueCountries.entrySet()) {
      sb.append(uniqueCountries.get(j++));
// to ensure a ',' is not appended at the end
      if(j != uniqueCountries.size()) {
        sb.append(",");
      }
    }
sb.append(":");
    
    int z = sb.length();
    while( i < n ) {
        sb.append(encoding.get(encoded[i++]));
// to ensure a ',' is not appended at the end
        if(i!=n) {
          sb.append(",");
        }
}
return sb.toString();
  }
public static String decode(final String input) {
   // Split the encoded string by country and it's code
    String[] countryCode = input.split(":");
    String[] countries = countryCode[0].split(",");
    String[] code = countryCode[1].split(",");
StringBuilder sb = new StringBuilder();
int n = code.length;
// decode the String using the respective country provided
    for(int i=0; i<n; i++) {
      sb.append(countries[Integer.parseInt(code[i])]);
if(i != n-1) {
          sb.append(",");
      }
    }
return sb.toString();
  }
public static void main(String[] args) {
    String input = "USA,USA,USA,USA,Mexico,Canada,Mexico,Mexico,Mexico,Argentina";
System.out.println(encode(input));
    System.out.println(decode(encode(input)));
  }
}

Output:

USA,Mexico,Canada,Argentina:0,0,0,0,1,2,1,1,1,3
USA,USA,USA,USA,Mexico,Canada,Mexico,Mexico,Mexico,Argentina

decode(encode(input)) = input string.