Fibonacci Number · Interview Problem

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Leetcode

Easy

Dynamic Programming

Recursion

Math

Fibonacci Number

Compute the n-th Fibonacci number in the sequence defined by the sum of the two previous terms.

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Problem Statement

Given a non-negative integer $n$ , return the $n$ -th Fibonacci number.

The Fibonacci sequence is defined as:

$F(0) = 0$
$F(1) = 1$
$F(n) = F(n - 1) + F(n - 2)$ for $n \ge 2$

This is a classic warm-up problem for practicing iterative computation, recursion, and dynamic programming.

Input Format

One integer $n$ .
$n$ is the index in the Fibonacci sequence.

Output Format

Return a single integer: $F(n)$ .

Constraints

$0 \le n$
The exact upper bound is platform-specific and not relied upon here.
Use a solution that is efficient enough for typical interview constraints.

Examples

Sample cases returned by the problem API.

Example 1

Input

n = 2

Output

Explanation

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

Example 2

Input

n = 5

Output

Explanation

The sequence starts 0, 1, 1, 2, 3, 5, so F(5) = 5.

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