Project Euler > Problem 117 > Red, green, and blue tiles (Java Solution)

Problem:

Using a combination of black square tiles and oblong tiles chosen from: red tiles measuring two units, green tiles measuring three units, and blue tiles measuring four units, it is possible to tile a row measuring five units in length in exactly fifteen different ways.



How many ways can a row measuring fifty units in length be tiled?

NOTE: This is related to problem 116.

Solution:

21124

Code:
The solution may include methods that will be found here: Library.java .

public interface EulerSolution{

public String run();

}

/* 
 * Solution to Project Euler problem 17
 * By Nayuki Minase
 * 
 * http://nayuki.eigenstate.org/page/project-euler-solutions
 * https://github.com/nayuki/Project-Euler-solutions
 */


public final class p017 implements EulerSolution {
	
	public static void main(String[] args) {
		System.out.println(new p017().run());
	}
	
	
	public String run() {
		int sum = 0;
		for (int i = 1; i <= 1000; i++)
			sum += toEnglish(i).length();
		return Integer.toString(sum);
	}
	
	
	private static String[] ONES = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"};  // Requires 0 <= n <= 9
	private static String[] TEENS = {"ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"};
	private static String[] TENS = {"twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"};
	
	
	// Requires 0 <= n <= 99999
	private static String toEnglish(int n) {
		if (n < 0 || n > 99999)
			throw new IllegalArgumentException();
		
		if (n < 100)
			return tens(n);
		else {
			String big = "";
			if (n >= 1000)
				big += tens(n / 1000) + "thousand";
			if (n / 100 % 10 != 0)
				big += ONES[n / 100 % 10] + "hundred";
			
			return big + (n % 100 != 0 ? "and" + tens(n % 100) : "");
		}
	}
	
	
	// Requires 0 <= n <= 99
	private static String tens(int n) {
		if (n < 10)
			return ONES[n];
		else if (n < 20)  // Teens
			return TEENS[n - 10];
		else
			return TENS[n / 10 - 2] + (n % 10 != 0 ? ONES[n % 10] : "");
	}
	
}