pairsThatSumUpToK Optimized

pairsThatSumUpToKOptimized

public static List<Pair> pairsThatSumUpToK(int[] a, int k) {
	HashSet<Integer> set = new HashSet<Integer>();
	List<Pair> result = new ArrayList<Pair>();
	for (int i = 0 ; i < a.length; i++) {
		int lookup = k - i;
		if (set.contains(lookup)) {
			result.add(new Pair(lookup, i));
		} else {
			set.add(i);
		}
	}

	return result;
}