509. Fibonacci Number

Easy

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).

Solution

class Solution:
    def fib(self, n: int) -> int:
        a = 0
        b = 1

        if n == 0:
            return a
        if n == 1:
            return b

        for i in range(2, n + 1):
            a, b = b, a + b

        return b