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Permutations by swapping: Difference between revisions
→{{header|Racket}}
(More general first D entry) |
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;Sample output:
The output is the same as before and is a list of all results rather than yielding each result from a generator function.
=={{header|Racket}}==
<lang Racket>
#lang racket
(define (add-at l i x)
(if (zero? i) (cons x l) (cons (car l) (add-at (cdr l) (sub1 i) x))))
(define (permutations l)
(define (loop l)
(cond [(null? l) '(())]
[else (for*/list ([(p i) (in-indexed (loop (cdr l)))]
[i ((if (odd? i) identity reverse)
(range (add1 (length p))))])
(add-at p i (car l)))]))
(for/list ([p (loop (reverse l))] [i (in-cycle '(1 -1))]) (cons i p)))
(define (show-permutations l)
(printf "Permutations of ~s:\n" l)
(for ([p (permutations l)])
(printf " ~a (~a)\n" (apply ~a (add-between (cdr p) ", ")) (car p))))
(for ([n (in-range 3 5)]) (show-permutations (range n)))
</lang>
Output:
<pre>
Permutations of (0 1 2):
0, 1, 2 (1)
0, 2, 1 (-1)
2, 0, 1 (1)
2, 1, 0 (-1)
1, 2, 0 (1)
1, 0, 2 (-1)
Permutations of (0 1 2 3):
0, 1, 2, 3 (1)
0, 1, 3, 2 (-1)
0, 3, 1, 2 (1)
3, 0, 1, 2 (-1)
3, 0, 2, 1 (1)
0, 3, 2, 1 (-1)
0, 2, 3, 1 (1)
0, 2, 1, 3 (-1)
2, 0, 1, 3 (1)
2, 0, 3, 1 (-1)
2, 3, 0, 1 (1)
3, 2, 0, 1 (-1)
3, 2, 1, 0 (1)
2, 3, 1, 0 (-1)
2, 1, 3, 0 (1)
2, 1, 0, 3 (-1)
1, 2, 0, 3 (1)
1, 2, 3, 0 (-1)
1, 3, 2, 0 (1)
3, 1, 2, 0 (-1)
3, 1, 0, 2 (1)
1, 3, 0, 2 (-1)
1, 0, 3, 2 (1)
1, 0, 2, 3 (-1)
</pre>
=={{header|Tcl}}==
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