CS61A_sp95_f - CS61A Spring 1995 Final CS61A Spring 1995...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
CS61A, Spring 1995 Final Question 1 (5 points): (a) Write a function prefix-to-infix that takes a Scheme arithmetic expression as its argument and returns a list containing the equivalent expression in the ordinary arithmetic notation with operators between the operands, like this: > (prefix-to-infix '(+ (* 2 3) (- 7 4))) ((2 * 3) + (7 - 4)) > (prefix-to-infix '(* (remainder 9 2) 5) ((9 remainder 2) * 5) You may assume that every function in the argument expression has exactly two arguments. (b) The procedure you wrote in part (a) carries out a tree reordering; in each sublist, the three elements are rearranged from the original order (0 1 2) to the new order (1 0 2) . That is, what used to be element number 1 now comes first; what used to be element number 0 now comes second, and what used to be number 2 remains third. We can represent this ordering by the list (1 0 2) . We'd like to generalize this by writing a procedure that takes an ordering as an additional argument, so that we could say (define (prefix-to-infix tree) (tree-reorder '(1 0 2) tree)) Here's an example of a tree-reorder that isn't a prefix-to-infix : > (tree-reorder '(2 1 2 1) '((a b c) (d e f) (g h i))) ((i h i h) (f e f e) (i h i h) (f e f e)) What follows is a partial implementation; your job is to fill in the blank. (define (tree-reorder ordering tree) (if (atom? tree) tree (map _______________________________________________________ ordering))) Assume that no number in the ordering is bigger than the length of any sublist; no error checking is needed. Question 2 (5 points): You are given a possibly infinite stream of lists of numbers. In the following example, the notation {...} represents a stream, while (...) represents a list: {(0 1 0 0 3) (1 2 3 0 4 2) (0 0 0 5 0) () (3) . ..} Write a procedure positions that, given such a stream as its argument, returns a stream of two-element lists showing the positions of the nonzero numbers within the argument. Each two-element list has the form CS61A: Spring 1995 Final 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
(list-number position-within-list) so for the stream shown above you would produce a stream with elements
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/23/2010 for the course CS 61A taught by Professor Harvey during the Fall '08 term at Berkeley.

Page1 / 5

CS61A_sp95_f - CS61A Spring 1995 Final CS61A Spring 1995...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online