A "Fibonacci" program is a job interview challenge: given an index number n, print its Fibonacci sequence term.
The Fibonacci sequence is a mathematical sequence in which each number is the sum of the two preceding ones: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, etc. For example, index number 0 is the sequence term 0, and index number 12 is the sequence term 144.
The example below defines a function named fibonacci. The function takes an input which is the Fibonacci sequence index number, and returns the Fibonacci sequence term number. For example, input index 0 returns term 0, and input index 12 returns term 144.
Example:
pub fn fibonacci(n: usize) -> usize {
match n {
0 => 0,
1 => 1,
2.. => fibonacci(n - 1) + fibonacci(n - 2),
_ => panic!("{}", n)
}
}
fn main() {
println!("{}", fibonacci(12));
}Output:
144
The "Fibonacci" program is frequently seen in programming for benchmarking, because the calculations and the recursions grow very quickly, and also because there are a variety of ways to optimize the program to run faster, to work without recursions, and to use less memory. For more about this, see the Rust Quick Guide page "Memoize a function with cached".