第N个泰波那契数

题源：leetcode

链接：https://leetcode-cn.com/problems/n-th-tribonacci-number/

最简单的动态规划

class Solution {
public:
    int tribonacci(int n) {
        if(n==0) return 0;
        if(n==1) return 1;
        int a = 0;
        int b = 1;
        int c = 1;
        int d = 1;
        for(int i = 2;i<n;i++){
            d = a+b+c;
            a = b;
            b = c;
            c = d;
        }

        return d;
    }
};