题目如下：

The 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) = 1F(N) = F(N - 1) + F(N - 2), for N > 1.

Given N, calculate F(N).

 

Example 1:

Input: 2Output: 1Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.

Example 2:

Input: 3Output: 2Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.

Example 3:

Input: 4Output: 3Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.

 

Note:

0 ≤ N ≤ 30.

解题思路：递归的经典例子，当然为了提高效率，可以缓存中间结果。这题好像以前是Premium的，最近解锁了。

代码如下：

class Solution(object):    def fib(self, N):        """        :type N: int        :rtype: int        """        if N == 0 or N == 1:            return N        return self.fib(N-1) + self.fib(N-2)