def fib(n, memo=None):
if n <= 1:
return n
return fib(n-1) + fib(n-2)
def fib(n, memo=None):
if memo is None:
memo = {}
if n <= 1:
return n
if n in memo:
return memo[n]
memo[n] = fib(n-1, memo) + fib(n-2, memo)
return memo[n]
30