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
Constraints:
0 <= n <= 37
- The answer is guaranteed to fit within a 32-bit integer, ie.
answer <= 2^31 - 1
.
Solution: DP
Time complexity: O(n)
Space complexity: O(n) -> O(1)
C++
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// Author: Huahua class Solution { public: int tribonacci(int n) { if (n == 0) return n; int t0 = 0; int t1 = 1; int t2 = 1; int t = 1; for (int i = 3; i <= n; ++i) { t = t0 + t1 + t2; t0 = t1; t1 = t2; t2 = t; } return t; } }; |
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