LeetCode： Fibonacci Number

Question

The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,

F(0) = 0, F(1) = 1 F(n) = F(n - 1) + F(n - 2), for n > 1. Given n, calculate F(n).

Example 1:

Input: n = 2

Output: 1

Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.

Example 2:

Input: n = 3

Output: 2

Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.

Example 3:

Input: n = 4

Output: 3

Explanation: F(4) = F(3) + F(2) = 2 + 1 = 2.

Constraints:

0 <= n <= 30

Solution #1

if n == 0
  return 0
elsif n == 1
  return 1
else
  return fib(n - 1) + fib(n - 2)
end

Solution #2

def fib(n)
    return n if n < 2
    fib(n-1) + fib(n-2)
end