剑指offer:]斐波那契数列(python)

f(n)=f(n-1)+f(n-2)

class Solution:
    def Fibonacci(self, n):
        if n==0:
            return 0
        if n==1 or n==2:
            return 1
        a,b=1,1
        for i in range(3,n+1):
            c=a+b
            a=b
            b=c
        return c