package test5;

import java.util.List;

public class Test5B 
{
    /**
     * Returns the conversion of the given string by replacing each
     * 0 (zero) with O (capital o) and each 1 with I.
     * 
     * @param binary a string of 0s and 1s
     * @pre. binary only consists of 0s and 1s
     * @return the conversion of the given string by replacing each
     * 0 (zero) with O (capital o) and each 1 with I.
     */
    public static String convert(String binary)
    {
	String convert;
	if (binary.length() == 0)
	{
	    convert = "";
	}
	else
	{
	    convert = (binary.charAt(0) == '0' ? "O" : "I") + Test5B.convert(binary.substring(1));
	}
	return convert;
    }
    
    /**
     * Returns the string consisting of the characters of the given list.
     * 
     * @param letters a list of characters
     * @pre. letters != null
     * @return the string consisting of the characters of the given list.
     */
    public static String concat(List<Character> letters)
    {
	return Test5B.concat(letters, 0);
    }
    
    /**
     * Returns the string consisting of the characters of the sub list
     * of the given list, beginning at the given index.
     * 
     * @param letters a list of characters
     * @pre. list != null
     * @param begin the begin index of the sub list
     * @pre. begin >= 0 && begin <= list.size()
     * @return the string consisting of the characters of the sub list
     * of the given list, beginning at the given index.
     */
    public static String concat(List<Character> letters, int begin)
    {
	String concat;
	if (letters.size() == begin)
	{
	    concat = "";
	}
	else
	{
	    concat = letters.get(begin) + Test5B.concat(letters, begin + 1);
	}
	return concat;
    }
}