Fibonacci Sequence in Java taking too long?

Question

I\'m trying to find the sum of the Fibonacci sequence in Java, but the run time is taking way too long (or is it suppose to?). This slows down anytime I use an integer past

Answer 1

For n > 2, an invocation of your getSum(n) recursively invokes itself twice. Each of those invocations may recurse further. The total number of method invocations scales as 2^n, and 2^50 is a very large number. This poor scaling reflects the fact that the simple-minded recursive approach ends up needlessly recomputing the same results (e.g. fib(4)) a great many times, and it is why your program slows down so rapidly as you increase n.

The negative return value you get after a certain point arises from exceeding the limits of data type int. You could get a larger limit with a wider data type, presumably long. If that's not enough then you would need to go to something like BigInteger, at a substantial performance penalty.