class Solution {
 
    public String encode(List<String> strs) {
        // Time Complexity = O(N)
        StringBuilder sb = new StringBuilder();
 
        char ch = '.'; // after each string from the list append a dot to segeregate
        for(String s : strs)
        {
            sb.append(s).append(ch);
        }
        return sb.toString();
    }
 
    public List<String> decode(String str) {
        // Time Complexity = O(N)
        List<String> list = new ArrayList<>();
 
        StringBuilder sb = new StringBuilder();
        for(char ch : str.toCharArray())
        {
            if(ch != '.')
                sb.append(ch);
 
            else 
            {
                // when dot is encountered, then add the current string to list
                list.add(sb.toString()); 
                // empty the current string
                sb = new StringBuilder();
            }
        }
        return list;
    }
}