a simple example of trade-off from fibonacci function to fast-fibonacci function

#old recursive fib function
def fib(n):
    if n == 0:
        return 1
    elif n == 1:
        return 1
    else:
        return fib(n-1)+fib(n-2)
print fib(100)

It is a good example to study recursion.

However, have you ever tried to compute a lare fibonacci number, like fibonacci(99),

using the recursive method? If you have not, I advise that you should not do that.

The only one goodness is that  it will waste of your patience. :)

To make a faster Fibonacci Function, people need spend some memory on saving time.

#new version Fib function
class fibDic(object):
    def __init__(self):
        self.dic = {}
    def isInfibDic(self,n):
        if n in self.dic:
            return True
        return False
    def getValue(self,n):
        return self.dic[n]
    def update(self,n,result):
        self.dic[n] = result
    
aDic = fibDic()
def fastfib(n,aDic):
    
    if aDic.isInfibDic(n):
        return aDic.getValue(n)
    else:
        if n == 0:
            result = 1
        elif n == 1:
            result = 1
        else:
            result = fastfib(n-1,aDic) +fastfib(n-2,aDic)
        aDic.update(n,result)
        return result
print fastfib(100,aDic)