Project Euler > Problem 91 > Right triangles with integer coordinates (Java Solution)

Problem:

The points P (x1, y1) and Q (x2, y2) are plotted at integer co-ordinates and are joined to the origin, O(0,0), to form ΔOPQ.


There are exactly fourteen triangles containing a right angle that can be formed when each co-ordinate lies between 0 and 2 inclusive; that is,
0 [≤] x1, y1, x2, y2 [≤] 2.


Given that 0 [≤] x1, y1, x2, y2 [≤] 50, how many right triangles can be formed?

Solution:

7652413

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

public interface EulerSolution{

public String run();

}

/* 
 * Solution to Project Euler problem 41
 * By Nayuki Minase
 * 
 * http://nayuki.eigenstate.org/page/project-euler-solutions
 * https://github.com/nayuki/Project-Euler-solutions
 */


public final class p041 implements EulerSolution {
	
	public static void main(String[] args) {
		System.out.println(new p041().run());
	}
	
	
	public String run() {
		for (int n = 9; n >= 1; n--) {
			int[] digits = new int[n];
			for (int i = 0; i < digits.length; i++)
				digits[i] = i + 1;
			
			int result = -1;
			do {
				if (Library.isPrime(toInteger(digits)))
					result = toInteger(digits);
			} while (Library.nextPermutation(digits));
			if (result != -1)
				return Integer.toString(result);
		}
		throw new RuntimeException("Not found");
	}
	
	
	private static int toInteger(int[] digits) {
		int result = 0;
		for (int x : digits)
			result = result * 10 + x;
		return result;
	}
	
}