练习2.41-练习2.47

1.练习2.41

(define (seprate-except x except)(filter (lambda (couple) (let ((first (car couple))(second (cadr couple)))(and (not (= first except))(not (= second except))(not (= first second)))))(map (lambda (n) (list n (- x n)))(enumerate-interval 1 (- x 1)))))(define (flatmap proc seq)(accumulate append '() (map proc seq)))(define (seprate-to-three n)(flatmap (lambda (x) (map (lambda (y) (cons x y)) (seprate-except (- n x) x)))(enumerate-interval 1 (- n 1))))

2.练习2.42

(define empty-board '())(define (adjoin-position new-row k rest-of-queens)(cons (list k new-row) rest-of-queens))(define (safe? k positions)(define (check-safe col row rest-positions)(if (null? rest-positions)true(let ((first-position-col (car (car rest-positions)))(first-position-row (cadr (car rest-positions)))(remain-positions (cdr rest-positions)))(and (not (= col first-position-col))(not (= row first-position-row))(not (= (abs (- col first-position-col))(abs (- row first-position-row))))(check-safe col row remain-positions)))))(if (null? positions)true(let ((col (car (car positions)))(row (cadr (car positions)))(rest (cdr positions)))(if (null? rest)true(check-safe col row rest)))))

3.练习2.43

因为重复计算k-1的皇后问题。

4.练习2.44

(require (planet "sicp.ss" ("soegaard" "sicp.plt" 2 1)))(define (up-split painter n)(if (= n 0)painter(let ((smaller (up-split painter (- n 1))))(below painter (beside smaller smaller)))))

5.练习2.45

(define (split action1 action2)(lambda (painter n)(if (= n 0)painter(let ((smaller ((split action1 action2) painter (- n 1))))(action1 painter (action2 smaller smaller))))))

6.练习2.46

(define (make-vect x y)(cons x y))(define (xcor-vect v)(car v))(define (ycor-vect v)(cdr v))(define (add-vect v1 v2)(make-vect (+ (xcor-vect v1)(xcor-vect v2))(+ (ycor-vect v1)(ycor-vect v2))))(define (sub-vect v1 v2)(make-vect (- (xcor-vect v1)(xcor-vect v2))(- (ycor-vect v1)(ycor-vect v2))))(define (scale-vect v s)(make-vect (* s (xcor-vect v))(* s (ycor-vect v))))

7.练习2.47

(define (make-frame-list origin edge1 edge2)(list origin edge1 edge2))(define (make-frame-cons origin edge1 edge2)(cons origin (cons edge1 edge2)))(define (origin-frame-list frame)(car frame))(define (edge1-frame-list frame)(cadr frame))(define (edge2-frame-list frame)(caddr frame))(define (origin-frame-cons frame)(car frame))(define (edge1-frame-cons frame)(cadr frame))(define (edge2-frame-cons frame)(cddr frame))

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