Lesson Plan - 6.001 SP04 - recitation 5

Data structures - abstraction

pictures!!!
box and pointer

value of (3 5 7)
value of (list 3 5 7)

cons
car
cdr
caddr - pick out 4
(7 6 5 4 3 2 1)

((7) (6 5 4) (3 2) 1)

(7 (6 (5 (4 (3 (2 (1)))))))

(7 ((6 5 ((4)) 3) 2) 1)

first,second,third
list - (list 1 2) same as (cons 1 (cons 2 nil))
list-ref
append

solutions:

prob1
(some pictures) printed reps:
(1 . 2)
(1 3 5)
(((3 . 2) 1 . 0))
(0 1 2)
((1 . 2) (4 5) 3)

prob2
(list 1 2 3) or (cons 1 (cons 2 (cons 3 nil)))
(cons 1 (cons 2 3))
(list (list 1 2) (list 3 4) (list 5 6))

prob3
(fourth lst) or (cadddr lst)
(third (second lst)) or (caddr (cadr lst))
(first (second (second (second lst)))) or (caadr (cadadr lst))
(first (first (third (first (second lst)))))

abstraction - self-delusion
mind games


class
-number
-units
-description

make-class
get-number
get-units
get-total-units
get-description

schedule
-classes

empty-schedule
add-class
remove-class
total-units

credit-limit