Lista 4

;; ćw. 6

(define (find-min t)
  (if (leaf? (node-left t))
      (node-val t)
      (find-min (node-left t))))

(define (find-max t)
  (if (leaf? (node-right t))
      (node-val t)
      (find-max (node-right t))))

(define (delete-min t)
  (if (leaf? (node-left t))
      (node-right t)
      (make-node (node-val t) (delete-min (node-left t)) (node-right t))))


(define (delete x t)
  (if (or (leaf? t) (not (bst-find x t)))
      t
      (cond [(> x (node-val t)) (make-node (node-val t)
                                           (node-left t)
                                           (delete x (node-right t)))]
            [(< x (node-val t)) (make-node (node-val t)
                                           (delete x (node-left t))
                                           (node-right t))]
            [else (let ((min (find-min (node-right t))))
                    (make-node min
                               (node-left t)
                               (delete-min (node-right t))))])))