计算Tribonaci队列

计算Tribonaci队列, 规则是T(n) = T(n - 1) + T(n - 2) + T(n -3)，其中T(0) = T(1) = 1，T(2) = 2。

/** Get the value of T(n - 1), and retrieve the result of T(n - 2) and T(n - 3).

@param[in] n The n in T(n).

@param[out] mid Value of T(n - 2).

@param[out] right Value of T(n - 3).

@return Value of T(n - 1).

*/

int find_trib(int n, int & mid, int & right)

{

if (3 == n)

{

mid = 1;

right = 1;

return 2;

}

else

{

int temp;

mid = find_trib(n - 1, right, temp);

return mid + right + temp;

}

}

/** Find value of T(n).

@param[in] The n in T(n).

@return Value of T(n).

@note T(n) = T(n - 1) + T(n - 2) + T(n - 3) (n > 2)

T(0) = T(1) = 1, T(2) = 2.

*/

int tribonaci(int n)

{

if (n <>{

return 0; // Undefined feature.

}

if (0 == n 1 == n)

{

return 1;

}
if (2 == n)

{

return 2;

}
int mid, right;

int left = find_trib(n, mid, right);

return left + mid + right;

}