1a)
(check-expect (column 0 fish-grid) '(B - - - B))
(check-expect (column 10 fish-grid) '(- - - - -))
(check-expect (column 11 fish-grid) '(B - - - -))
(check-expect (column 21 fish-grid) empty)

1b)
(check-expect (cells->tallies '(B - - - B - B B - B))
              (list 1 1 2 1))
(check-expect (cells->tallies '(- - B B B B - B B - B))
              (list 4 2 1))
(check-expect (cells->tallies '(B B B B B B B B))
              (list 8))
(check-expect (cells->tallies '(- - - - - - -))
              empty)
(check-expect (cells->tallies '())
              empty)

1c)
(check-expect (puzzle-labels (list '(B B -)
                                   '(- - B)
                                   '(B - B)))
              (list (list (list 2)
                          (list 1)
                          (list 1 1))
                    (list (list 1 1)
                          (list 1)
                          (list 2))))
(check-expect (puzzle-labels (list '(B B - - B)
                                   '(- B - B -)
                                   '(- - - - -)
                                   '(B B B B B)
                                   '(B - B - B)))
              (list (list (list 2 1)
                          (list 1 1)
                          empty
                          (list 5)
                          (list 1 1 1))
                    (list (list 1 2)
                          (list 2 1)
                          (list 2)
                          (list 1 1)
                          (list 1 2))))
(check-expect (puzzle-labels (list '(- - - -)
                                   '(- - - -)
                                   '(- - - -)
                                   '(- - - -)))
              (list (list empty
                          empty
                          empty
                          empty)
                    (list empty
                          empty
                          empty
                          empty)))
(check-expect (puzzle-labels (list '(-)))
              (list (list empty)
                    (list empty)))

2a)
(check-expect (bst-count (make-node 9
                         (make-node 7 empty (make-node 8 empty empty))
                         (make-node 10 empty empty))) 4)
(check-expect (bst-count (make-node 10 (make-node 9 (make-node 7 empty
                                                    (make-node 8 empty empty))
                                       empty)
                                       (make-node 11 empty
                                       (make-node 12 empty empty)))) 6)
(check-expect (bst-count empty) 0)

2b)
(check-expect (bst-add 7 my-bst)
 (make-node 5 (make-node 3 empty empty)
              (make-node 9 (make-node 7 empty empty) empty)))
(check-expect (bst-add 6 my-bst)
 (make-node 5 (make-node 3 empty empty)
              (make-node 9 (make-node 7
                           (make-node 6 empty empty) empty) empty)))
(check-expect (bst-add 10 my-bst)
 (make-node 5 (make-node 3 empty empty) (make-node 9
               (make-node 7 empty empty)
               (make-node 10 empty empty))))
(check-expect (bst-add 0 my-bst)
 (make-node 5 (make-node 3 (make-node 0 empty empty) empty) (make-node 9
               (make-node 7 empty empty) empty)))

2c)
(check-expect (bst-height my-bst) 2)
(check-expect (bst-height (make-node 9
                          (make-node 7 empty (make-node 8 empty empty))
                          (make-node 10 empty empty))) 2)
(check-expect (bst-height (make-node 10 (make-node 9 (make-node 7 empty
                                        (make-node 8 empty empty))
                                        empty)
                                        (make-node 11 empty
                                        (make-node 12 empty empty)))) 3)
(check-expect (bst-height empty) 0)

2d)
(check-expect (bst-balanced? (make-node 9
                             (make-node 7 empty (make-node 8 empty empty))
                             (make-node 10 empty empty))) true)
(check-expect (bst-balanced? (make-node 10 (make-node 9 (make-node 7 empty
                                           (make-node 8 empty empty))
                                           empty)
                                           (make-node 11 empty
                                           (make-node 12 empty empty))))
              true)
(check-expect (bst-balanced? empty) true)
(check-expect (bst-balanced? (make-node 10
                             (make-node 9 (make-node 8 empty empty)
                              empty)
                              empty))
              false)
(check-expect (bst-balanced? (make-node 5
                             (make-node 3
                             (make-node 1 (make-node 0 empty empty) empty)
                              empty) empty)) false)