Given a list of numbers and a number k, return whether any two numbers from the list add up to k.

Problem1.java

public boolean problem1(List<Integer> numberList, int k) {
	Map<Integer, Integer> differenceToNumberMap = new HashMap<>();
	for (Integer number : numberList) {
		if (number != null) {
			if (differenceToNumberMap.containsKey(number)) {
				return true;
			} else {
				differenceToNumberMap.put(k - number, number);
			}
		}
	}
	return false;
}