【剑指offer】1-斐波那契数列(Python & C++)

题目描述：

大家都知道斐波那契数列，现在要求输入一个整数n，请你输出斐波那契数列的第n项（从0开始，第0项为0）。

Python

方法一：递归法，但超时

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

方法二：

class Solution:
    def Fibonacci(self, n):
        if n == 0:
            return 0
        if n == 1:
            return 1
        if n > 1:
            a1,a2 = 0,1
            a = 0
            for i in range(1,n):
                a = a1 + a2
                a1,a2 = a2,a
            return a

方法三

# -*- coding:utf-8 -*-
class Solution:
    def Fibonacci(self, n):
        # write code here
        res=[0,1,1,2]
        while len(res)<=n:
            res.append(res[-1]+res[-2])
        return res[n]

方法三

# -*- coding:utf-8 -*-
class Solution:
    def Fibonacci(self, n):
        # write code here
        if n == 0:
            return 0
        if n == 1:
            return 1
        if n == 2:
            return 1
        if n >= 3:
            s = []*n
            s.append(1)
            s.append(1)
            for i in xrange(2,n):
                s.append(s[i-1]+s[i-2])
            return s[n-1]

C++

动态规划

class Solution {
public:
    int Fibonacci(int n) {
        int f = 0, g = 1;
        while(n--) {
            g += f;
            f = g - f;
        }
        return f;
    }
};