he 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.
- code
class Solution:
def fib(self, N: int) -> int:
a, b = 0, 1
for i in range(N): a, b = b, a + b
return a
- code
class Solution:
def fib(self, n: int) -> int:
cache = {0:0,1:1}
def helper(n):
if n in cache:
return cache[n]
cur = helper(n-1) + helper(n-2)
cache[n] = cur
return cur
return helper(n)