diff options
Diffstat (limited to 'net')
| -rw-r--r-- | net/ricketyspace/sicp/two/fortytwo.scm | 40 |
1 files changed, 38 insertions, 2 deletions
diff --git a/net/ricketyspace/sicp/two/fortytwo.scm b/net/ricketyspace/sicp/two/fortytwo.scm index e284591..af5b500 100644 --- a/net/ricketyspace/sicp/two/fortytwo.scm +++ b/net/ricketyspace/sicp/two/fortytwo.scm @@ -4,7 +4,8 @@ (define-module (net ricketyspace sicp two fortytwo) #:export (safe? - adjoin-position)) + adjoin-position + queens)) (define (accumulate op initial sequence) (if (null? sequence) @@ -24,7 +25,7 @@ (car pos)) (define (position-col pos) - (car (cdr pos))) + (cdr pos)) (define (abs-diff pos-a pos-b) (cons (abs (- (position-row pos-a) (position-row pos-b))) @@ -58,3 +59,38 @@ (define (adjoin-position new-row k rest-of-queens) (let ((queen-at-k (cons new-row k))) (append rest-of-queens (list queen-at-k)))) + +(define empty-board '()) + +(define (queens board-size) + (define (queen-cols k) + (if (= k 0) + (list empty-board) + (filter + (lambda (positions) (safe? k positions)) + (flatmap + (lambda (rest-of-queens) + (map (lambda (new-row) + (adjoin-position new-row k rest-of-queens)) + (enumerate-interval 1 board-size))) + (queen-cols (- k 1)))))) + (queen-cols board-size)) + +;;; +;;; Guile REPL +;;; +;;; scheme@(guile-user)> ,use (net ricketyspace sicp two fortytwo) +;;; scheme@(guile-user)> (queens 8) +;;; $2 = (((1 . 1) (5 . 2) (8 . 3) (6 . 4) (3 . 5) (7 . 6) (2 . 7) (4 . 8)) ((1 . 1) (6 . 2) (8 . 3) (3 . 4) (7 . 5) (4 . 6) (2 . 7) (5 . 8)) ((1 . 1) (7 . 2) (4 . 3) (6 . 4) (8 . 5) (2 . 6) (5 . 7) (3 . 8)) ((1 . 1) (7 . 2) (5 . 3) (8 . 4) (2 . 5) (4 . 6) (6 . 7) (3 . 8)) ((2 . 1) (4 . 2) (6 . 3) (8 . 4) (3 . 5) (1 . 6) (7 . 7) (5 . 8)) ((2 . 1) (5 . 2) (7 . 3) (1 . 4) (3 . 5) (8 . 6) (6 . 7) (4 . 8)) ((2 . 1) (5 . 2) (7 . 3) (4 . 4) (1 . 5) (8 . 6) (6 . 7) (3 . 8)) ((2 . 1) (6 . 2) (1 . 3) (7 . 4) (4 . 5) (8 . 6) (3 . 7) (5 . 8)) ((2 . 1) (6 . 2) (8 . 3) (3 . 4) (1 . 5) (4 . 6) (7 . 7) (5 . 8)) ((2 . 1) (7 . 2) (3 . 3) (6 . 4) (8 . 5) (5 . 6) (1 . 7) (4 . 8)) ((2 . 1) (7 . 2) (5 . 3) (8 . 4) (1 . 5) (4 . 6) (6 . 7) (3 . 8)) ((2 . 1) (8 . 2) (6 . 3) (1 . 4) (3 . 5) (5 . 6) (7 . 7) (4 . 8)) ((3 . 1) (1 . 2) (7 . 3) (5 . 4) (8 . 5) (2 . 6) (4 . 7) (6 . 8)) ((3 . 1) (5 . 2) (2 . 3) (8 . 4) (1 . 5) (7 . 6) (4 . 7) (6 . 8)) ((3 . 1) (5 . 2) (2 . 3) (8 . 4) (6 . 5) (4 . 6) (7 . 7) (1 . 8)) ((3 . 1) (5 . 2) (7 . 3) (1 . 4) (4 . 5) (2 . 6) (8 . 7) (6 . 8)) ((3 . 1) (5 . 2) (8 . 3) (4 . 4) (1 . 5) (7 . 6) (2 . 7) (6 . 8)) ((3 . 1) (6 . 2) (2 . 3) (5 . 4) (8 . 5) (1 . 6) (7 . 7) (4 . 8)) ((3 . 1) (6 . 2) (2 . 3) (7 . 4) (1 . 5) (4 . 6) (8 . 7) (5 . 8)) ((3 . 1) (6 . 2) (2 . 3) (7 . 4) (5 . 5) (1 . 6) (8 . 7) (4 . 8)) ((3 . 1) (6 . 2) (4 . 3) (1 . 4) (8 . 5) (5 . 6) (7 . 7) (2 . 8)) ((3 . 1) (6 . 2) (4 . 3) (2 . 4) (8 . 5) (5 . 6) (7 . 7) (1 . 8)) ((3 . 1) (6 . 2) (8 . 3) (1 . 4) (4 . 5) (7 . 6) (5 . 7) (2 . 8)) ((3 . 1) (6 . 2) (8 . 3) (1 . 4) (5 . 5) (7 . 6) (2 . 7) (4 . 8)) ((3 . 1) (6 . 2) (8 . 3) (2 . 4) (4 . 5) (1 . 6) (7 . 7) (5 . 8)) ((3 . 1) (7 . 2) (2 . 3) (8 . 4) (5 . 5) (1 . 6) (4 . 7) (6 . 8)) ((3 . 1) (7 . 2) (2 . 3) (8 . 4) (6 . 5) (4 . 6) (1 . 7) (5 . 8)) ((3 . 1) (8 . 2) (4 . 3) (7 . 4) (1 . 5) (6 . 6) (2 . 7) (5 . 8)) ((4 . 1) (1 . 2) (5 . 3) (8 . 4) (2 . 5) (7 . 6) (3 . 7) (6 . 8)) ((4 . 1) (1 . 2) (5 . 3) (8 . 4) (6 . 5) (3 . 6) (7 . 7) (2 . 8)) ((4 . 1) (2 . 2) (5 . 3) (8 . 4) (6 . 5) (1 . 6) (3 . 7) (7 . 8)) ((4 . 1) (2 . 2) (7 . 3) (3 . 4) (6 . 5) (8 . 6) (1 . 7) (5 . 8)) ((4 . 1) (2 . 2) (7 . 3) (3 . 4) (6 . 5) (8 . 6) (5 . 7) (1 . 8)) ((4 . 1) (2 . 2) (7 . 3) (5 . 4) (1 . 5) (8 . 6) (6 . 7) (3 . 8)) ((4 . 1) (2 . 2) (8 . 3) (5 . 4) (7 . 5) (1 . 6) (3 . 7) (6 . 8)) ((4 . 1) (2 . 2) (8 . 3) (6 . 4) (1 . 5) (3 . 6) (5 . 7) (7 . 8)) ((4 . 1) (6 . 2) (1 . 3) (5 . 4) (2 . 5) (8 . 6) (3 . 7) (7 . 8)) ((4 . 1) (6 . 2) (8 . 3) (2 . 4) (7 . 5) (1 . 6) (3 . 7) (5 . 8)) ((4 . 1) (6 . 2) (8 . 3) (3 . 4) (1 . 5) (7 . 6) (5 . 7) (2 . 8)) ((4 . 1) (7 . 2) (1 . 3) (8 . 4) (5 . 5) (2 . 6) (6 . 7) (3 . 8)) ((4 . 1) (7 . 2) (3 . 3) (8 . 4) (2 . 5) (5 . 6) (1 . 7) (6 . 8)) ((4 . 1) (7 . 2) (5 . 3) (2 . 4) (6 . 5) (1 . 6) (3 . 7) (8 . 8)) ((4 . 1) (7 . 2) (5 . 3) (3 . 4) (1 . 5) (6 . 6) (8 . 7) (2 . 8)) ((4 . 1) (8 . 2) (1 . 3) (3 . 4) (6 . 5) (2 . 6) (7 . 7) (5 . 8)) ((4 . 1) (8 . 2) (1 . 3) (5 . 4) (7 . 5) (2 . 6) (6 . 7) (3 . 8)) ((4 . 1) (8 . 2) (5 . 3) (3 . 4) (1 . 5) (7 . 6) (2 . 7) (6 . 8)) ((5 . 1) (1 . 2) (4 . 3) (6 . 4) (8 . 5) (2 . 6) (7 . 7) (3 . 8)) ((5 . 1) (1 . 2) (8 . 3) (4 . 4) (2 . 5) (7 . 6) (3 . 7) (6 . 8)) ((5 . 1) (1 . 2) (8 . 3) (6 . 4) (3 . 5) (7 . 6) (2 . 7) (4 . 8)) ((5 . 1) (2 . 2) (4 . 3) (6 . 4) (8 . 5) (3 . 6) (1 . 7) (7 . 8)) ((5 . 1) (2 . 2) (4 . 3) (7 . 4) (3 . 5) (8 . 6) (6 . 7) (1 . 8)) ((5 . 1) (2 . 2) (6 . 3) (1 . 4) (7 . 5) (4 . 6) (8 . 7) (3 . 8)) ((5 . 1) (2 . 2) (8 . 3) (1 . 4) (4 . 5) (7 . 6) (3 . 7) (6 . 8)) ((5 . 1) (3 . 2) (1 . 3) (6 . 4) (8 . 5) (2 . 6) (4 . 7) (7 . 8)) ((5 . 1) (3 . 2) (1 . 3) (7 . 4) (2 . 5) (8 . 6) (6 . 7) (4 . 8)) ((5 . 1) (3 . 2) (8 . 3) (4 . 4) (7 . 5) (1 . 6) (6 . 7) (2 . 8)) ((5 . 1) (7 . 2) (1 . 3) (3 . 4) (8 . 5) (6 . 6) (4 . 7) (2 . 8)) ((5 . 1) (7 . 2) (1 . 3) (4 . 4) (2 . 5) (8 . 6) (6 . 7) (3 . 8)) ((5 . 1) (7 . 2) (2 . 3) (4 . 4) (8 . 5) (1 . 6) (3 . 7) (6 . 8)) ((5 . 1) (7 . 2) (2 . 3) (6 . 4) (3 . 5) (1 . 6) (4 . 7) (8 . 8)) ((5 . 1) (7 . 2) (2 . 3) (6 . 4) (3 . 5) (1 . 6) (8 . 7) (4 . 8)) ((5 . 1) (7 . 2) (4 . 3) (1 . 4) (3 . 5) (8 . 6) (6 . 7) (2 . 8)) ((5 . 1) (8 . 2) (4 . 3) (1 . 4) (3 . 5) (6 . 6) (2 . 7) (7 . 8)) ((5 . 1) (8 . 2) (4 . 3) (1 . 4) (7 . 5) (2 . 6) (6 . 7) (3 . 8)) ((6 . 1) (1 . 2) (5 . 3) (2 . 4) (8 . 5) (3 . 6) (7 . 7) (4 . 8)) ((6 . 1) (2 . 2) (7 . 3) (1 . 4) (3 . 5) (5 . 6) (8 . 7) (4 . 8)) ((6 . 1) (2 . 2) (7 . 3) (1 . 4) (4 . 5) (8 . 6) (5 . 7) (3 . 8)) ((6 . 1) (3 . 2) (1 . 3) (7 . 4) (5 . 5) (8 . 6) (2 . 7) (4 . 8)) ((6 . 1) (3 . 2) (1 . 3) (8 . 4) (4 . 5) (2 . 6) (7 . 7) (5 . 8)) ((6 . 1) (3 . 2) (1 . 3) (8 . 4) (5 . 5) (2 . 6) (4 . 7) (7 . 8)) ((6 . 1) (3 . 2) (5 . 3) (7 . 4) (1 . 5) (4 . 6) (2 . 7) (8 . 8)) ((6 . 1) (3 . 2) (5 . 3) (8 . 4) (1 . 5) (4 . 6) (2 . 7) (7 . 8)) ((6 . 1) (3 . 2) (7 . 3) (2 . 4) (4 . 5) (8 . 6) (1 . 7) (5 . 8)) ((6 . 1) (3 . 2) (7 . 3) (2 . 4) (8 . 5) (5 . 6) (1 . 7) (4 . 8)) ((6 . 1) (3 . 2) (7 . 3) (4 . 4) (1 . 5) (8 . 6) (2 . 7) (5 . 8)) ((6 . 1) (4 . 2) (1 . 3) (5 . 4) (8 . 5) (2 . 6) (7 . 7) (3 . 8)) ((6 . 1) (4 . 2) (2 . 3) (8 . 4) (5 . 5) (7 . 6) (1 . 7) (3 . 8)) ((6 . 1) (4 . 2) (7 . 3) (1 . 4) (3 . 5) (5 . 6) (2 . 7) (8 . 8)) ((6 . 1) (4 . 2) (7 . 3) (1 . 4) (8 . 5) (2 . 6) (5 . 7) (3 . 8)) ((6 . 1) (8 . 2) (2 . 3) (4 . 4) (1 . 5) (7 . 6) (5 . 7) (3 . 8)) ((7 . 1) (1 . 2) (3 . 3) (8 . 4) (6 . 5) (4 . 6) (2 . 7) (5 . 8)) ((7 . 1) (2 . 2) (4 . 3) (1 . 4) (8 . 5) (5 . 6) (3 . 7) (6 . 8)) ((7 . 1) (2 . 2) (6 . 3) (3 . 4) (1 . 5) (4 . 6) (8 . 7) (5 . 8)) ((7 . 1) (3 . 2) (1 . 3) (6 . 4) (8 . 5) (5 . 6) (2 . 7) (4 . 8)) ((7 . 1) (3 . 2) (8 . 3) (2 . 4) (5 . 5) (1 . 6) (6 . 7) (4 . 8)) ((7 . 1) (4 . 2) (2 . 3) (5 . 4) (8 . 5) (1 . 6) (3 . 7) (6 . 8)) ((7 . 1) (4 . 2) (2 . 3) (8 . 4) (6 . 5) (1 . 6) (3 . 7) (5 . 8)) ((7 . 1) (5 . 2) (3 . 3) (1 . 4) (6 . 5) (8 . 6) (2 . 7) (4 . 8)) ((8 . 1) (2 . 2) (4 . 3) (1 . 4) (7 . 5) (5 . 6) (3 . 7) (6 . 8)) ((8 . 1) (2 . 2) (5 . 3) (3 . 4) (1 . 5) (7 . 6) (4 . 7) (6 . 8)) ((8 . 1) (3 . 2) (1 . 3) (6 . 4) (2 . 5) (5 . 6) (7 . 7) (4 . 8)) ((8 . 1) (4 . 2) (1 . 3) (3 . 4) (6 . 5) (2 . 6) (7 . 7) (5 . 8))) +;;; scheme@(guile-user)> (length $2) +;;; $3 = 92 +;;; scheme@(guile-user)> (list-ref $2 (random 93)) +;;; $4 = ((5 . 1) (2 . 2) (6 . 3) (1 . 4) (7 . 5) (4 . 6) (8 . 7) (3 . 8)) +;;; scheme@(guile-user)> (list-ref $2 (random 93)) +;;; $5 = ((4 . 1) (6 . 2) (1 . 3) (5 . 4) (2 . 5) (8 . 6) (3 . 7) (7 . 8)) +;;; scheme@(guile-user)> (list-ref $2 (random 93)) +;;; $6 = ((7 . 1) (2 . 2) (4 . 3) (1 . 4) (8 . 5) (5 . 6) (3 . 7) (6 . 8)) +;;; scheme@(guile-user)> (list-ref $2 (random 93)) +;;; $7 = ((6 . 1) (3 . 2) (1 . 3) (8 . 4) (5 . 5) (2 . 6) (4 . 7) (7 . 8)) +;;; scheme@(guile-user)> (list-ref $2 (random 93)) +;;; $8 = ((4 . 1) (8 . 2) (5 . 3) (3 . 4) (1 . 5) (7 . 6) (2 . 7) (6 . 8)) |