Working solution to the 2016 AP Computer Science Free Response Question String Formatter - https://compsci.rocks/string-formatter-solution/

LeftOverSpaces.java

public static int leftoverSpaces( List<String> wordList, int formattedLen ) {
    /* Implementation not shown */
    return formattedLen - totalLetters( wordList ) - ( basicGapWidth( wordList, formattedLen ) * wordList.size() - 1 );
}

PartA.java

public static int totalLetters( List<String> wordList ) {
    /* Part A */
    int let = 0;
    for ( String word : wordList ) {
        let += word.length();
    }
    return let;
}

PartB.java

public static int basicGapWidth( List<String> wordList, int formattedLen ) {
    /* Part B */
    return ( formattedLen - totalLetters( wordList ) ) / ( wordList.size() - 1 );
}

PartC.java

public static String format( List<String> wordList, int formattedLen ) {
    /* Part C */
    int width = basicGapWidth( wordList, formattedLen );
    int leftoverRemaining = leftoverSpaces( wordList, formattedLen );

    String formatted = "";
    for ( int i = 0; i < wordList.size() - 1; i++ ) {
        formatted += wordList.get( i );

        for ( int s = 1; s <= width; s++ ) {
            formatted += " ";
        }

        if ( leftoverRemaining > 0 ) {
            formatted += " ";
            leftoverRemaining--;
        }
    }

    formatted += wordList.get( wordList.size() - 1 );

    return formatted.trim();
}

StringFormatter_Starter.java

public class StringFormatter {
    public static int totalLetters( List<String> wordList ) {
        /* Part A */
    }
    
    public static int basicGapWidth( List<String> wordList, int formattedLen ) {
        /* Part B */
    }

    public static int leftoverSpaces( List<String> wordList, int formattedLen ) {
        /* Implementation not shown */
    }

    public static String format( List<String> wordList, int formattedLen ) {
        /* Part C */
    }
}