Leetcode 509. Fibonacci Number

Problem

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).

Algorithm

Calculated using the recursive formula.

Code

class Solution:
    def fib(self, n: int) -> int:
        if n < 2:
            return n

        Fn_2, Fn_1, = 0, 1
        for i in range(2, n+1):
            Fn = Fn_1 + Fn_2
            Fn_2 = Fn_1
            Fn_1 = Fn
        
        return Fn