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