JavaAlgorithms/ProjectEuler/Problem07.java

package ProjectEuler;

/**
 * By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is
 * 13.
 *
 * <p>What is the 10 001st prime number?
 *
 * <p>link: https://projecteuler.net/problem=7
 */
public class Problem07 {
  public static void main(String[] args) {
    int[][] testNumbers = {
      {1, 2},
      {2, 3},
      {3, 5},
      {4, 7},
      {5, 11},
      {6, 13},
      {20, 71},
      {50, 229},
      {100, 541}
    };
    for (int[] number : testNumbers) {
      assert solution1(number[0]) == number[1];
    }
  }

  /***
   * Checks if a number is prime or not
   * @param number the number
   * @return {@code true} if {@code number} is prime
   */
  private static boolean isPrime(int number) {
    if (number == 2) {
      return true;
    }
    if (number < 2 || number % 2 == 0) {
      return false;
    }
    for (int i = 3, limit = (int) Math.sqrt(number); i <= limit; i += 2) {
      if (number % i == 0) {
        return false;
      }
    }
    return true;
  }

  private static int solution1(int n) {
    int count = 0;
    int number = 1;

    while (count != n) {
      if (isPrime(++number)) {
        count++;
      }
    }
    return number;
  }
}