finonacci.py

# 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


class Solution:
    def fib(self, n: int, memo = {}) -> int:
        if n == 0 or n == 1:
            return n
        if not memo.get(n):
            memo[n] = self.fib(n - 1, memo) + self.fib(n - 2, memo)
        return memo[n]