public class Solution {
    public String joinWithSeparator(String[] arr, String separator) {
        // Une los elementos del array con el separador dado
        StringBuilder output = new StringBuilder();

        for (int i = 0; i < arr.length; i++){
            output.append(arr[i]);
            if(i < arr.length -1){
                output.append(separator);
            }
        }
        return output.toString();

    }
}