(struct tree (left value right) #:transparent)

(define (imbalance tree n)
  (if (null? tree)
      #t

      (letrec ([visina (lambda (x)
                (cond [(null? x) 1]
                      [(and (null? (tree-left x)) (null? (tree-right x))) 2]
                      [(null? (tree-left x)) (+ 1 (visina (tree-right x)))]
                  [(null? (tree-left x)) (+ 1 (visina tree-left))]
                  [#t (+ 1 (max (visina (tree-left x)) (visina (tree-right x))))]))]
               [visina_levo (visina (tree-left tree))]
               [visina_desno (visina (tree-right tree))])
        (if (> (abs (- visina_levo visina_desno)) n)
            #f
            (begin (imbalance (tree-left tree) n)
                   (imbalance (tree-right tree) n))))))