Question

I learn lisp a few days ago, and I want to do is like following

1 `(1 2 3 4 1 5) ==> ( 2 3 4 1 5)

What I cand do is to remove all the occurence, I cannot figure out how to preserve the last symbol.

here is my code

(defun test (X L)
  (cond ((null L) nil)
        ((equal X (last L)) (test X (butlast L)))    
        (t (cons (test X (butlast L)) (last L)))))

Thx for your reading my question !

Answer 1

Here you go, recursive, but not very efficient solution:

(defun remove-all-but-last (X L)
    (cond ((null L) nil)
           ((equal X (car L)) 
               (if (member X (cdr L)) 
                   (remove-all-but-last X (cdr L)) 
                   L)) 
           (t (cons (car L) (remove-all-but-last X (cdr L))))))