两个清单作为生产清单的输入-方案

Question

供参考，我正在使用DrRacket使用Scheme进行编程。

我正在尝试使功能全部tally-by-all该功能消耗list-of-candidates list-of-votes list-of-voting-tallies ，以借助已经定义的helper函数输出list-of-votes tally-by-all list-of-candidates top-votes-for 。

当我按原样运行时，会发生错误，因为辅助函数top-votes-for消耗了一个string和一个list-of-votes因此它不能完全消耗一个list-of-strings来代替string ，至少我还是这样想。

我应该得到的输出是：

(cons (make-voting-tally "Blake" 2)
(cons (make-voting-tally "Ash" 0)
(cons (make-voting-tally "Bob" 1)
(cons (make-voting-tally "Will" 0)
(cons (make-voting-tally "Joey" 0) empty))))))

请记住，程序中的所有内容都是正确的，除非定义了tally-by-all 。

任何帮助将不胜感激。

先感谢您！

这是我的程序：

;; Data Definition
(define-struct vote (choice1 choice2 choice3))
;; A vote is a structure: (make-vote String String String). 
;; interp. 3 candidates that one person has voted for (String).

(define vote1
  (make-vote "Blake" "Joey" "Will"))

(define vote2
  (make-vote "Blake" "Bob" "Ash"))

(define vote3
  (make-vote "Bob" "Ash" "Blake"))

(define listofVotes
  (list vote1 vote2 vote3))

;; Signature: top-votes-for: string list-of-strings -> number
;; Purpose: Consumes a name and a list of votes and produces the number of
;;          times that the given name was the first choice vote in the list of votes.
;;          (This tallies points under winner-takes-all strategy.)
;; Tests:
(check-expect (top-votes-for "Blake" empty) 0)
(check-expect (top-votes-for "Blake" listofVotes) 2)
(check-expect (top-votes-for "Bob" listofVotes) 1)
(check-expect (top-votes-for "Ash" listofVotes) 0)
(check-expect (top-votes-for "Joey" listofVotes) 0)
(check-expect (top-votes-for "Will" listofVotes) 0)
;; Define:
(define (top-votes-for cand alov)
  (cond
    [(empty? alov) 0]
    [(string=? (vote-choice1 (first alov)) cand) (+ 1 (top-votes-for cand (rest alov)))]
    [else (top-votes-for cand (rest alov))]
    )
  )

;; Data Definition
(define-struct voting-tally (candidate numVotes))
;; A voting-tally is a structure: (make-voting-tally String Number). 
;; interp. a candidate (String) and how many votes said
;;         candidate has gotten (Number).

(define listofCandidates
  (list "Blake" "Ash" "Bob" "Will" "Joey"))

;; Signature: tally-by-all: list-of-canidates list-of-votes -> list-of-Voting-Tallies
;; Purpose: Consumes a list of candidate names and a list of votes and produces a
;;          list of voting-tallies.
;; Tests:
(check-expect (tally-by-all empty empty) empty)
(check-expect (tally-by-all listofCandidates listofVotes) (cons (make-voting-tally "Blake" 2)
                                                          (cons (make-voting-tally "Ash" 0)
                                                          (cons (make-voting-tally "Bob" 1)
                                                          (cons (make-voting-tally "Will" 0)
                                                          (cons (make-voting-tally "Joey" 0) 
                                                                 empty))))))
;; Define:
(define (tally-by-all aloc alov)
  (cond
    [(empty? alov) empty]
    [else (cons (make-voting-tally (first aloc) (tally-by-all alov (rest (top-votes-for aloc alov)))))]
    )
  )

Answer 1

我认为您想要的是对候选人列表（ aloc ）进行递归，并针对每个候选人，从所有投票中计算出他/她的得分：

(define (tally-by-all aloc alov)
  (cond
    [(empty? aloc) empty]
    [else (cons (make-voting-tally (first aloc) (top-votes-for (first aloc) alov))
                (tally-by-all (rest aloc) alov)))]
    )
  )