codeChallenge/Alone.java

public class Alone {
  public static void main(String[] args) {

    int[] ar = { 1, 1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 4, 4, 5, 6, 6, 6, 7, 7, 7, 8, 8, 8, 9 };
    lonelyNum(ar);
  }

  public static void lonelyNum(int[] arr) {
    for (int i = 0; i < arr.length; i++) {
      int count = 0;

      for (int k = 0; k < arr.length; k++) {
        if (arr[i] == arr[k]) {
          count++;
        }
      }
      if (count == 1) {
        System.out.println(arr[i]);
      }
    }
  }
}