劍指offer第7題 牛客網線上程式設計連結 https://www.nowcoder.com/activity/oj
斐波那契數列

題目描述
要求輸入一個整數n，請你輸出斐波那契數列的第n項（從0開始，第0項為0）。n<=39

思路1：遞迴
當n = 0時，Fibonacci = 0；當n = 1時，Fibonacci = 1；當n >= 2時，Fibonacci(n) = Fibonacci(n - 1) + Fibonacci(n - 2)

Python2.7編寫

# -*- coding:utf-8 -*-
class Solution:
    def Fibonacci(self, n):
        if n == 0:
            return 0
        elif n == 1:
            return 1
        else:
            return self.Fibonacci(n - 1) + self.Fibonacci(n - 2)
 

思路2：遞迴的解法效率太低，用迭代的方法解決

Python2.7編寫

# -*- coding:utf-8 -*-
class Solution:
    def Fibonacci(self, n):
        f = 0
        g = 1
        if n == 0:
            return 0
        elif n == 1:
            return 1
        else:
            for i in range(2,n+1):
                f,g = g,f + g
        return g