leetcode 1137

class Solution {
public:
    int tribonacci(int n) {
        int result = 0;
        if ( n <= 1 )
        {
            return n;
        }
        if ( n == 2 )
        {
            return 1;
        }
        int val_n_3 = 0;
        int   val_n_2 = 1;
        int   val_n_1 = 1;
        int temp = 0;
        for ( int i = 3; i <= n; i++ )
        {
            

            temp = val_n_3 + val_n_2 + val_n_1;
            val_n_3 = val_n_2;
            val_n_2 = val_n_1;
            val_n_1 = temp;
            
        }
        result = temp;
        return temp;
    }
};