1137. N Th Tribonacci Number · LeetCode Solutions

Problem Statement

1137. N-th Tribonacci Number

Easy

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.

C++

Source file

class Solution {
public:
    vector<int> dp = {0, 1, 1};
    int tribonacci(int n) {
        if(n<dp.size())   return dp[n];
        dp.push_back(tribonacci(n-3)+tribonacci(n-2)+tribonacci(n-1));
        return dp.back();
    }
};