fork download
copy 
  1. ; powerset
  2.  
  3. (define (power-set xs)
  4.   (if (null? xs) (list (list))
  5.     (let ((rest (power-set (cdr xs))))
  6.       (append rest (map (lambda (x) (cons (car xs) x)) rest)))))
  7.  
  8. (display (power-set '(1 2 3))) (newline)
  9.  
  10. (define (bits n len)
  11.   (let loop ((n n) (len len) (bs (list)))
  12.     (if (zero? len) bs
  13.       (loop (quotient n 2) (- len 1)
  14.             (cons (if (odd? n) 1 0) bs)))))
  15.  
  16. (define (collect n xs)
  17.   (let loop ((bs (bits n (length xs))) (xs xs) (zs (list)))
  18.     (if (null? bs) zs
  19.       (loop (cdr bs) (cdr xs)
  20.         (if (zero? (car bs)) zs (cons (car xs) zs))))))
  21.  
  22. (define (power-set xs)
  23.   (do ((n 0 (+ n 1)) (xss (list) (cons (collect n xs) xss)))
  24.       ((= n (expt 2 (length xs))) xss)))
  25.  
  26. (display (power-set '(1 2 3))) (newline)
  27.  
  28. (define (for-power-set op xs)
  29.   (let ((len (length xs)))
  30.     (do ((n 0 (+ n 1))) ((= n (expt 2 len)))
  31.       (op (collect n xs)))))
  32.  
  33. (for-power-set (lambda (s) (display s) (newline)) '(1 2 3))
Success #stdin #stdout 0.01s 7280KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
(() (3) (2) (2 3) (1) (1 3) (1 2) (1 2 3))
((3 2 1) (2 1) (3 1) (1) (3 2) (2) (3) ())
()
(3)
(2)
(3 2)
(1)
(3 1)
(2 1)
(3 2 1)
https://ideone.com/MBPxVm
language:
()
created:
8 years ago
visibility:
secret

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!