Hi,
I need to write a non-recursive version of the function sum-squares and Use a do-loop that is based on the length of the argument list.
+1
A:
Here's how it's done generally:
(defun sum-squares (list) (loop for x in list
for y = (* x x)
summing y into total
finally (return total)))
A do loop solution is even simpler, but not half as elegant:
(defun sum-squares (list)
(let ((sum 0)) (do ((i 0 (1+ i)))
((>= i (length list)))
(setq sum (+ sum (* (nth i list) (nth i list)))))
sum))
Bozhidar Batsov
2010-04-21 06:14:59
Thanks a lot...
bubdada
2010-04-21 06:42:26
Why not (loop for x in list summing (* x x)). Any your do loop solution is O(n^2); try iterating directly on the list items, instead of the indices.
huaiyuan
2010-04-21 06:55:24
+ 1 from me for the great comment. I wrote the loop especially verbose, so that the example could show the full structure of a loop construct - I thought it might be informative to a beginner in this manner. As for the second example - orcik wanted a solution that used the length of the argument list - otherwise I would have surely iterated over the elements themselves.
Bozhidar Batsov
2010-04-21 07:50:52