Task:

 Generate a string with   N   opening brackets   [   and with   N   closing brackets   ],   in some arbitrary order. 
 Determine whether the generated string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order), none of which mis-nest.


Examples

   (empty)      OK
   []           OK   
   [][]         OK   
   [[][]]       OK 
   ][         NOT OK
   ][][       NOT OK
   []][[]     NOT OK



mata
function random_brackets(n) {
	return(invtokens(("[","]")[runiformint(1,2*n,1,2)],""))
}
 
function is_balanced(s) {
	n = strlen(s)
	if (n==0) return(1)
	a = runningsum(92:-ascii(s))
	return(all(a:>=0) & a[n]==0)
}
end