Memoized Fibonacci Numbers with Java 8

MemoizedFibonacci.java

static Map<Integer,Long> memo = new HashMap<>();

static {
  memo.put(0,0L);
	memo.put(1,1L);
}
	
public static long fibonacci(int x) {
  return memo.computeIfAbsent(x, n -> Math.addExact(fibonacci(n-1), fibonacci(n-2)));
}