Fibonacci sequence for n > 46 Java

Question

I have the following code which provides the correct values for n < 47.

public static int fib(int n) {
    int nthTerm = 0;
    if (n == 2)
        nthTerm =          


        

Answer 1

The reason you can't use int is because fib(47) is 2971215073 which overflows Java's signed 32-bit int (231-1). You could use a memoization optimization to implement it with BigInteger like,

private static Map memo = new HashMap<>();
static {
    memo.put(0, BigInteger.ZERO);
    memo.put(1, BigInteger.ONE);
}

public static BigInteger fib(int n) {
    if (memo.containsKey(n)) {
        return memo.get(n);
    }
    BigInteger v = fib(n - 2).add(fib(n - 1));
    memo.put(n, v);
    return v;
}