Balanced brackets: Difference between revisions

=={{header|Common Lisp}}==

<lang lisp>(defun string-of-brackets (n)

(let ((result (make-string (* 2 n)))

(opening n)

(closing n))

(dotimes (i (* 2 n) result)

(setf (aref result i)

(cond

((zerop opening) #\])

((zerop closing) #\[)

(t (if (= (random 2) 0)

(progn (decf opening) #\[)

(progn (decf closing) #\]))))))))

(defun balancedp (string)

(zerop (reduce (lambda (nesting bracket)

(ecase bracket

(#\] (if (= nesting 0)

(return-from balancedp nil)

(1- nesting)))

(#\[ (1+ nesting))))

string

:initial-value 0)))

(defun show-balanced-brackets ()

(dotimes (i 10)

(let ((s (string-of-brackets i)))

(format t "~3A: ~A~%" (balancedp s) s))))</lang>

Output:

<pre>CL-USER> (show-balanced-brackets)

T :

NIL: ][

T : [[]]

NIL: []]][[

T : [][][][]

NIL: []][]][[[]

NIL: []]]]][][[[[

NIL: ][]]]]][[[[][[

T : [[[[[[][[]]]]]]]

NIL: ]][[[[][]][[[[]]]]

</pre>