PARTIAL SOLUTIONS to RECURSIVE PRACTICE PROBLEMS

These are some solutions to the more difficult problems. I’ll put up more variabtions when I get a chance.

(define (number-everything-embedded sent)

(nee-helper 1 sent))

(define (nee-helper cur sent)

(if (empty? sent)

'()

(se (word cur ': (first sent))

(nee-helper (+ cur 1) (bf sent)))))

(define (number-everything-tail sent)

(net-helper 1 sent '()))

(define (net-helper cur sent so_far)

(if (empty? sent)

so_far

(net-helper (+ cur 1) (bf sent) (se so_far (word cur ': (first sent))))))

(define (wave-maker v p c)

(if (= c 0)

""

(word (make-one-wave-e v p) (wave-maker v p (- c 1)))))

(define (make-one-wave-e v p)

(if (= v p)

(word p p)

(word v (make-one-wave-t (+ v 1) p) v)))

(define (make-one-wave-t v p)

(mow-t-helper v p "" ""))

(define (mow-t-helper v p lh rh)

(if (= v p)

(word lh p p rh)

(mow-t-helper (+ v 1) p (word lh v) (word v rh))))

(define (partition pivot sent)

(part-t-help pivot sent '() '() '()))

(define (part-t-help pivot sent l e g)

(cond ((empty? sent) (sentence l e g))

((< (first sent) pivot) (part-t-help pivot (bf sent) (se l (first sent)) e g))

((< pivot (first sent)) (part-t-help pivot (bf sent) l e (se g (first sent))))

(else (part-t-help pivot (bf sent) l (se e (first sent)) g))))

(define (adds-to-n n sent)

(cond ((= n 0) #t)

((empty? sent) #f)

(else (or (adds-to-n (- n (first sent)) (bf sent))

(adds-to-n n (bf sent))))))

(define (exactly-n-a-words n sent)

(cond ((empty? sent) (= n 0))

((a-word? (first sent)) (exactly-n-a-words (- n 1) (bf sent)))

(else (exactly-n-a-words n (bf sent)))))

(define (a-word? word)

(equal? (first word) 'a))