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

Input: n = 4
Output: 4
Explanation:
T_3 = 0 + 1 + 1 = 2
T_4 = 1 + 1 + 2 = 4

Solution

/**
 * @param {number} n
 * @return {number}
 */
var tribonacci = function(n) {
    //Declare an array of size n+1 and fill it with 0
    let dp = new Array(n+1).fill(0);
    dp[1] = 1
    dp[2] = 1;
    for(let i =3; i<=n; i++){
        //The tribonacci number at index i is the sum of the previous 3 tribonacci numbers
        dp[i] = dp[i-1] + dp[i-2] +dp[i-3]
    }
    //Return the tribonacci number at index n
    return dp[n]
};