题解 | #贪吃牛#

# 啊终于有我会的动态规划题了
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param n int整型 
# @return int整型
#
class Solution:
    def eatGrass(self , n: int) -> int:
        # write code here
        if n == 1 or n == 2:
            return n
        # O(n)方法
        # grass = [1, 2]
        # for i in range(2, n):
        #     grass.append(grass[i-1] + grass[i-2])
        
        # return grass[-1]
        
        # O(1)方法
        grass1 = 1
        grass2 = 2
        for i in range(2, n):
            grass = grass1 + grass2
            grass1 = grass2
            grass2 = grass

        return grass2