1137.n-th-tribonacci-number.cpp

/*
 * @lc app=leetcode id=1137 lang=cpp
 *
 * [1137] N-th Tribonacci Number
 */

// @lc code=start
class Solution
{
public:
    int tribonacci(int n)
    {

        if (n == 0)
            return 0;
        if (n == 1)
            return 1;
        if (n == 2)
            return 1;

        int a = 0, b = 1, c = 1, d = 0;
        for (int i = 3; i <= n; i++)
        {
            d = a + b + c;
            a = b;
            b = c;
            c = d;
        }
        return d;
    }
};
// @lc code=end