【leetcode】1137. N-th Tribonacci Number

题目如下：

The Tribonacci sequence Tn is defined as follows:

T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2for 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
Constraints:

0 <= n <= 37

The answer is guaranteed to fit within a 32-bit integer, ie. answer <= 2^31 - 1.

解题思路：动态规划入门级的题目。

代码如下：

class Solution(object):

    fib_list = []

    def tribonacci(self, n):

        """

        :type n: int

        :rtype: int

        """

        f = [0,1,1]

        if len(self.fib_list) == 0:

            for i in range(0,38):

                if i <= 2:

                    self.fib_list.append(f[i])

                    continue

                self.fib_list.append(self.fib_list[-1] + self.fib_list[-2] + self.fib_list[-3])

        return self.fib_list[n]

巴特西

【leetcode】1137. N-th Tribonacci Number

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