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;;   Lab3 -- Solutions

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;; PROBLEM 2:  Problems on lists-of-numbers
;;


;; minimum: list-of-numbers -> number
;; find minimum value on alon
;; (define (minimum alon) ... ) 

;;;;;;;  Examples
; "(minimum empty) answer:  empty"
; "(minimum '(-2)) answer: -2"
; "(minimum '(27 11 -2 5 -4)) answer:  -4)"

;;;;;;;;Template for functions on list-of-numbers
;(define (fun-on-a-lons a-lons)
;    (cond
;	[(empty? a-lons) ...]
;	[else
;	   (first a-lons) ...
;	   (fun-on-a-lons (rest a-lons)) ...]))

;;;;;;; Body

    ;; Need to consider (empty? rest a-lons)
    ;;     Consider what happens to (minimum (cons -2 empty))
(define (minimum a-lons)
  (cond
    [(empty? a-lons) 'empty]
    [(empty? (rest a-lons)) (first lons)]  
    [(< (first a-lons) 
	(minimum (rest a-lons))) 
              (first a-lons )] ))

;;;;;;; Tests
"(minimum empty) answer:  empty"
(minimum empty)
"(minimum '(-2)) answer: -2"
(minimum '(-2))
"(minimum '(27 11 -2 5 -4)) answer:  -4)"
(minimum '(27 11 -2 5 -4))



;; remove-nums: list-of-numbers number -> list-of-numbers
;; remove all numbers less than a-num from a-lons
;; (define (remove-nums alon a-num) ... )


;;;;;;;  Examples
; "(remove-nums empty 5) answer:  empty"
; "(remove-nums '(2 8) 5) answer: '(8)"
; "(remove-nums '(7 12) 5) answer: '(7 12)"
; "(remove-nums '(5) 5) answer: '(5)"

;;;;;;;;Template 
;;;;;;;;  Template for function with extra parameters besides a-lons
;(define (fun2-on-a-lons a-lons a-num)
;    (cond
;	[(empty? a-lons) ...]
;	[else
;	   (first a-lons) ...
;	   (fun-on-a-lons (rest a-lons) a-num) ...]))

;;;;;;; Body
(define (remove-nums a-lons a-num)
    (cond
	[(empty? a-lons) a-lons]
	[(<  (first a-lons) a-num)  (remove-nums (rest a-lons) a-num)]
	[ else    ;;; (first a-lons) belongs on list
	   (cons (first a-lons) (remove-nums (rest a-lons) a-num)) ]))

;;;;;;; Tests
 "(remove-nums empty) answer:  empty"
   
(remove-nums empty 5)
 "(remove-nums '(2 8) 5) answer: '(8)"
(remove-nums '(2 8) 5)
 "(remove-nums '(7 12) 5) answer: '(7 12)"
(remove-nums '(7 12) 5)
 "(remove-nums '(5) 5) answer: '(5)"
(remove-nums '(5) 5)
   
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;;
;; PROBLEM 3:  Help Your Grader
;;


;; a student is a
;; (make-student symbol symbol)
(define-struct student (name grade)) 

; constructor:  make-student
; predicate:  student?
; selectors:  student-name student-grade

;;;;;;;  Basic Templates for functions on Students:

;;;;; Template for Function on Student
;;;;      A student is a compound data object
; (define (fun-for-stud stud)
;    ... (student-name stud) ...
;    ... (student-grade stud) ... )

;;;; Template for Function on lists-of-students
;;;;    Template calls fun-for-stud
; (define (fun-for-alost a-lost)
;    (cond
;        [(empty? alost) ...]
;        [else
;            ... (fun-for-stud (first a-lost)) ...
;            ... (fun-for-alost (rest a-lost)) ...]))


;; get-grade: list-of-students symbol -> symbol
;; given alost and name (of student) return grade if student on list
;; Return 'None if student not on list
;; (define (get-grade alost name) ...)

;;;;;;;;Examples
;; "(get-grade empty 'ken), answer: 'None"
;; "(get-grade (list (make-student 'ken 'A) 
;                    (make-student 'robby 'B)
;                    (make-student 'jacob 'C))
;               'ken), answer: 'A"
;; "(get-grade (list (make-student 'ken 'A) 
;                    (make-student 'robby 'B)
;                    (make-student 'jacob 'C))
;               'kate), answer: 'None"

;;;;;;;; Body

;;;; Template for Function on lists-of-students
;;;;    with one parameter
;;;;    See Template fun-for-stud
; (define (fun-for-alost2 a-lost a-name)
;    (cond
;        [(empty? alost) ...]
;        [else
;            ... (fun-for-stud (first a-lost)) ...
;            ... (fun-for-alost2 (rest a-lost) a-name) ...]))

(define (get-grade alost name)
  (cond
    [(empty? alost) 'none]
    [(symbol=? name (student-name (first alost))) 
     (student-grade (first alost))]
    [else 
     (get-grade (rest alost) name)]))


;;;;;;;; Tests

 "(get-grade empty 'ken), answer: 'None"
(get-grade empty 'ken)
 "(get-grade (list (make-student 'ken 'A) 
                    (make-student 'robby 'B)
                    (make-student 'jacob 'C))
               'ken), answer: 'A"

(get-grade (list (make-student 'ken 'A) 
                    (make-student 'robby 'B)
                    (make-student 'jacob 'C))
	   'ken)
	
 "(get-grade (list (make-student 'ken 'A) 
                    (make-student 'robby 'B)
                    (make-student 'jacob 'C))
               'kate), answer: 'None"
(get-grade (list (make-student 'ken 'A) 
                    (make-student 'robby 'B)
                    (make-student 'jacob 'C))
            'kate)

	   
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;;
;;      I leave the following for you to practice.
;;      
	
;; get-names: list-of-students symbol -> list-of-symbols
;; Return list of all names of students with given grade
;; (define (get-names alost grade)...)

;; update-grade: list-of-students name grade -> list-of-students
;; update alost by changing student-grade to grade for name
;; (define (update-student alost name grade) ... )

   
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;;
;; PROBLEM 4:  Binary-to-Decimal
;;
	
	

;; bin->dec: list-of-bits -> number
;; convert alob to decimal value, assuming alob starts from least
;; significant bit to most significant bit
;; (define (bin->decs alob) ... )

;;;;;;;;;; Examples
;; "(bin->dec empty), answer: 0
;; "(bin->dec '(1)), answer: 1
;; "(bin->dec '(0 1)), answer: 2
;; "(bin->dec '(1 0 1 1)), answer:  13

;;;;;;;;Template for functions on list-of-numbers
;(define (fun-on-a-lons a-lons)
;    (cond
;	[(empty? a-lons) ...]
;	[else
;	   (first a-lons) ...
;	   (fun-on-a-lons (rest a-lons)) ...]))	
	
(define (bin->dec a-lons) 
  (cond
    [(empty? a-lons) 0]
    [else 
     (+ (first a-lons)
        (* 2 (bin->dec (rest a-lons))))]))

;;;;;;;;;; Tests
 "(bin->dec empty), answer: 0"
(bin->dec empty)
 "(bin->dec '(1)), answer: 1"
(bin->dec '(1))
 "(bin->dec '(0 1)), answer: 2"
(bin->dec '(0 1))
 "(bin->dec '(1 0 1 1)), answer:  13"
(bin->dec '(1 0 1 1))

   
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