Project Euler > Problem 6 > Sum square difference (Java Solution)

Problem:

The sum of the squares of the first ten natural numbers is,

12 + 22 + ... + 102 = 385

The square of the sum of the first ten natural numbers is,

(1 + 2 + ... + 10)2 = 552 = 3025

Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025 [−] 385 = 2640.

Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.

Solution:

25164150

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

public interface EulerSolution{

public String run();

}

/* 
 * Solution to Project Euler problem 6
 * By Nayuki Minase
 * 
 * http://nayuki.eigenstate.org/page/project-euler-solutions
 * https://github.com/nayuki/Project-Euler-solutions
 */


public final class p006 implements EulerSolution {
 
 public static void main(String[] args) {
  System.out.println(new p006().run());
 }
 
 
 private static final int N = 100;
 
 
 public String run() {
  int sum = 0;
  int sum2 = 0;
  for (int i = 1; i <= N; i++) {
   sum += i;
   sum2 += i * i;
  }
  /* 
   * For the mathematically inclined:
   *   sum  = N(N + 1) / 2.
   *   sum2 = N(N + 1)(2N + 1) / 6.
   */
  return Integer.toString(sum * sum - sum2);
 }
 
}