# Solving Leetcode Interviews in Seconds with AI: Fibonacci Number


	# Introduction
	In this blog post, we will explore how to solve the LeetCode problem "509" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like [Chatmagic](https://www.chatmagic.app), we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

	# Problem Statement
	> 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  

	# Explanation
	*   **Iterative Approach:** Calculate Fibonacci numbers iteratively using a loop, avoiding recursion to enhance efficiency.
*   **Constant Space:** Store only the two most recent Fibonacci numbers, minimizing memory usage.

*   Runtime Complexity: O(n), Storage Complexity: O(1)

	
	# Code
	```python
	def fib(n: int) -> int:
    """
    Calculate the nth Fibonacci number.

    Args:
        n: The index of the Fibonacci number to calculate.

    Returns:
        The nth Fibonacci number.
    """
    if n <= 1:
        return n

    a = 0
    b = 1

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

    return b
	```