N-th Tribonacci Number

给一个数字n, 返回三位bonacci数.

class Solution {
    public int tribonacci(int n) {
        int[] dp = new int[n+1];
        if(n == 0)
            return 0;
        if(n == 1)
            return 1;
        if(n == 2)
            return 1;
        dp[0] = 0;
        dp[1] = 1;
        dp[2] = 1;
        for(int i = 3; i <=n; i++){
            dp[i] = dp[i-1] + dp[i-2] + dp[i-3];
        }
        return dp[n];
    }
}