Fibonacci Number Python Solution with Tests

LeetCode 509, Easy. Topics: Math, Dynamic Programming, Recursion, Memoization. View on LeetCode. Generate this problem as a practice environment: tested reference solution, 18 parametrized pytest cases, and a playground notebook:

lcpy gen -n 509   # by problem number
lcpy gen -s fibonacci_number   # by problem name

Problem

The Fibonacci numbers, commonly denoted <code>F(n)</code> form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from <code>0</code> and <code>1</code>. That is, <pre> F(0) = 0, F(1) = 1 F(n) = F(n - 1) + F(n - 2), for n > 1. </pre> Given <code>n</code>, calculate <code>F(n)</code>.

Examples

Input: n = 2
Output: 1
Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.

Input: n = 3
Output: 2
Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.

Input: n = 4
Output: 3
Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.

Constraints

0 <= n <= 30

Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

class Solution:
    # Time: O(n)
    # Space: O(1)
    def fib(self, n: int) -> int:
        prev, curr = 0, 1
        for _ in range(n):
            prev, curr = curr, prev + curr
        return prev

Complexity

Time	Space
O(n)	O(1)

Welcome

Getting Started

Practice

CLI

Catalog

Contributing

Troubleshooting

Fibonacci Number Python Solution with Tests

Problem

Examples

Constraints

Solution

Complexity

Tags

​Problem

​Examples

​Constraints

​Solution

​Complexity

​Tags

Problem

Examples

Constraints

Solution

Complexity

Tags