0509. Fibonacci Number

https://leetcode.com/problems/fibonacci-number

Description

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 = 3.

Constraints:

• 0 <= n <= 30

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