Given a set of week days and a positive integer K, find the week of day which follows a day plus K days.

WeekOfDayNextToK.java

/**
 * Given the next set of week of days as strings in the given order: <code>Mon, Tue, Wed, Thu, Fri, Sat, Sun</code> <br/>
 * and given a positive integer <code>K</code> in the range <code>[0..500]</code>. <br/>
 * Find the week of day for a given day plus K days.<br/>
 * For example:<br/>
 * <code>Wed + 5 = Mon</code>
 * <code>Sun + 0 = Sun</code>
 * <code>Tue + 28 = Tue</code>
 * <br/><br/>
 * Max time for resolution: 15 minutes.
 */
class WeekOfDayNextToK {

	private int daysOfWeekCount = 7;
	private String[] daysOfWeek = new String[] { "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun" };
	
	public static void main(String[] args) {
		
		WeekOfDayNextToK solution = new WeekOfDayNextToK();
		
		System.out.println(solution.solution("Wed", 5)); // Mon
		System.out.println(solution.solution("Sun", 0)); // Sun
		System.out.println(solution.solution("Tue", 28)); // Tue
	}
	
	public String solution(String S, int K) {

		// find index of S
		int indexOfS = getIndexForDay(S, daysOfWeek);
		
		// apply module over K to get the offset
		int indexForSPlusK = (indexOfS + K) % daysOfWeekCount;
		
		return daysOfWeek[indexForSPlusK];
	}

	private int getIndexForDay(String S, String[] daysOfWeek) {
		for (int i=0, c=daysOfWeek.length; i < c; ++i) {
			if (daysOfWeek[i].equals(S)) {
				return i;
			}
		}
		return 0;
	}

}