$(9\%)$ To find the $n$th term of the sequence defined by $a_0=1,a_1=2,a_2=3,$ and $a_n=a_{n-1}+a_{n-2}+a_{n-3},$ for $n=3,4,5,$dots, we can use a recursive algorithm or an iterative algorithm.

$($a$)(3\%)$ Please devise a recursive algorithm to achieve this goal.

$($b$)(3\%)$ Please devise an iterative algorithm to achieve this goal.

$($c$)(3\%)$ Is the recursive or the iterative algorithm for finding the sequence more efficient?