Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 30

Description

N-th Tribonacci Number

The Tribonacci sequence T_n is defined as follows: 

T₀ = 0, T₁ = 1, T₂ = 1, and T_n+3 = T_n + T_n+1 + T_n+2 for n >= 0.

Given n, return the value of T_n.

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

struct Table{
  constexpr Table() : values() {
    values[0] = 0;
    values[1] = 1;
    values[2] = 1;
    for(int i = 3; i < 38; ++i) {
      values[i] = values[i - 1] + values[i - 2] + values[i - 3];
    }
  }
  int values[38] = {};
};
constexpr auto table = Table();
class Solution {
public:
  int tribonacci(int n) {
    return table.values[n];
  }
};

// Accepted
// 39/39 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 47.39 % of cpp submissions (5.9 MB)