import java.util.ArrayList;

import java.util.List;

public class Solution {

/*

* @param strs: a list of strings

* @return: encodes a list of strings to a single string.

*/

public String encode(List<String> strs) {

List<String> temp = new ArrayList<>();

if(strs.size() == 0) return null;

for(String s : strs) {

if(":".equals(s)) {

temp.add("::");

} else {

temp.add(s);

}

}

return String.join(":;", temp);

}

/*

* @param str: A string

* @return: decodes a single string to a list of strings

*/

public List<String> decode(String str) {

List<String> temp = new ArrayList<>();

if(str == null) return new ArrayList<>();

// if(str.length() == 0) return new ArrayList<>();

for(String s : str.split(":;")) {

if("::".equals(s)) {

temp.add(":");

} else {

temp.add(s);

}

}

return temp;

}

}