题解 | 牛牛学数列6
牛牛学数列6
https://www.nowcoder.com/practice/b6321648517247b2ac2e2f80cbc63ae1
import sys
n= int(input())
y = 0
lst = []
if n == 1:
y = 0
print(y)
elif 2<= n <=3:
y = 1
print(y)
else:
a1,a2,a3 = 0,1,1
for i in range(4,n+1):
a_nest = a1 + 2*a2 +a3
a1,a2,a3 = a2,a3,a_nest
print(a_nest)
