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Postby Goheeca » Tue Oct 13, 2015 3:30 am

I would decompose it to two problems.
  1. filling in to the rectangle
  2. transposing

Code: Select all
(define (repeat n elem)
    (if (= n 0)
        (cons elem (repeat (- n 1) elem))))

(define (fill-list lst len elem)
    (if (>= (length lst) len)
        (append lst (repeat (- len (length lst)) elem))))

(define (make-rectangle data with)
    (map (lambda (row)
            (fill-list row (apply max (map length data)) with))

Code: Select all
(define (transpose data)
    (apply map list data))

Code: Select all
(define (solution data)
    (transpose (make-rectangle data '())))

Here it is on

What concerns recursive thinking, there are three main parts in a simple recursion:
  1. condition of termination -- e.g. null?
  2. tail value/elementar operation -- e.g. '()
  3. recursive computation itself (processing of an element + compounding of the results)
  4. -- e.g. (cons (process ...) ...)
During the construction of an recursive function try to ask how these parts look like and then it should be easy.
cl-2dsyntax is my attempt to create a Python-like reader. My mirror of CLHS (and the dark themed version). Temporary mirrors of aferomentioned: CLHS and a dark version.
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