描述
The Tribonacci sequence Tn is defined as follows:
T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2 for n >= 0.
Given n, return the value of Tn.
Example 1:
Input: n = 4
Output: 4
Explanation:
T_3 = 0 + 1 + 1 = 2
T_4 = 1 + 1 + 2 = 4
Example 2:
Input: n = 25
Output: 1389537
Note:
0 <= n <= 37
The answer is guaranteed to fit within a 32-bit integer, ie. answer <= 2^31 - 1.
解析
根据题意，就是求出来第 n 个 Tribonacci 数，而 Tribonacci 数的计算方法是如题所述，按照定义写代码即可。
解答
class Solution(object):
def tribonacci(self, n):
"""
:type n: int
:rtype: int
"""
T = [0, 1, 1]
for i in range(3, n+1):
T.append(T[i-1]+T[i-2]+T[i-3])
return T[n]
运行结果
Runtime: 16 ms, faster than 71.03% of Python online submissions for N-th Tribonacci Number.
Memory Usage: 13.5 MB, less than 31.03% of Python online submissions for N-th Tribonacci Number.
原题链接：leetcode.com/problems/n-…
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