Test if 2 numbers contained in an array add up to a given number. The time complexity is n(n-1)/2. Space complexity is constant.

ArraySum.java

public class ArraySum {

  private int[] array = new int[]{1,2,3,4,5,6,7,8,9};

	/**
	 * Do any 2 add up to this number
	 * @param number
	 * @return
	 */
	public boolean canAdd(int number){
		for(int i=0;i<array.length;i++){
			for(int j=i+1;j<array.length;j++){
				System.out.println("Adding " + array[i] + " and  " + array[j]);
				if(array[i]+array[j]==number) {
					System.out.println("The numbers " + array[i] + " and " + array[j] + " add up to " + number);
					return true;
				}
			}
		}
		return false;
	}
	
	public static void main(String[] args) {
		new ArraySum().canAdd(7+8);
	}

}