方法没有返回正确的答案？还有人输入吗？

Question

在这种方法中，我应该返回选举的获胜者。这是通过重复使用candidatesWithFewest() 方法来完成的，直到只有一个候选人（得票最多）。您通过成为选票上的名字获得选票。如果两名或多名候选人获得相同数量的第一名选票，则选举不是决定性的。我的错误是，当两个或多个候选人拥有相同数量的第一名选票时，它仍然会返回其中一个候选人。我所有的其他方法都返回正确的输出，所以我相信问题出在getWinner 方法中。 CandidateWithFewest 返回所有得票最少的候选人的列表。我想从名单中删除这些候选人，直到只剩下一名候选人。

    /**
    * Returns the winner of the election using the candidatesWithFewest()
    * method.If there is no winner method returns a statement stating the
    * election is not decisive.
    *
    * @param vbal VoterBallots object
    * @param candList a list of candidate names
    * @return the winner of the election
    */
    public String getWinner(VoterBallots vbal, ArrayList<String> candList) {
        // Run rounds until down to a single candidate
        while (candList.size() > 2) { 
            ArrayList<String> loser = vbal.candidatesWithFewest(candList);
            String listString = "";

            for (String s : loser) {
                listString += s;
                candList.remove(listString);         
            }          
        }

        if (candList.size() > 0) { 
            return candList.iterator().next(); // Return the surviving candidate
        } else {
            return "Election is non decisive.";
        }
    }

    /**
    * Returns a list of one or more candidates tied with the fewest
    * first choice votes
    *
    * Precondition: each String in candidateList appears exactly once
    * in each Ballot in ballotList
    *
    * @param candidateList a list of candidate names
    *
    * @return a list of those candidates tied with the fewest first
    * choice votes
    */
    public ArrayList<String> candidatesWithFewest(ArrayList<String> candidateList) {
        ArrayList<String> losers = new ArrayList<String>(); //empty list for losers
        int minTally = ballotList.size() + 1;      //number of min votes
        for (int can = 0; can < candidateList.size(); can++) {
            String candidate = candidateList.get(can);
            // // number of first place votes
            int votes = numFirstVotes(candidate, candidateList);
            if (votes < minTally) {
                minTally = votes;
                losers = new ArrayList<String>(); // adds loser to list
            }
            if (votes == minTally) {
                losers.add(candidateList.get(can)); //adds losers with the same vote
            }
        }
        return losers;  // returns list of candidates with fewest votes
    }
   /**
     * Returns the number of times a given candidate appears first, among those
     * elements that are on candidateList, among all elements of ballotList
     * (i.e., among all ballots)
     *
     * @param candidate the name of a candidate
     * @param candidateList a list of candidate names Precondition: candidate
     * appears in candidateList
     * @return the number of times that candidate is first among those in
     * candidateList for all elements of ballotList
     */
    public int numFirstVotes(String candidate, ArrayList<String> candidateList) 
        // implementation not shown
        {
            int numVotes = 0;
            for (Ballot voterBallot : ballotList) {
                String first = voterBallot.firstChoiceFrom(candidateList);
                if (candidate.equals(first)) {
                    numVotes++;
                }
            }
            return numVotes;
    }
    /**
     * @param candidateList a list of candidate names
     * @return the name of the first choice candidate for this Ballot from those
     * in candidateList
     */
        public String firstChoiceFrom(ArrayList<String> candidateList) {

        for (String firstChoice : ballot) {
           if(candidateList.contains(firstChoice))
           {
           return firstChoice;
           }          

    }
        return null; // does not appear on candidate list
}
}

Answer 1

我猜是代码 sn-p ：

for (String s : loser) {
            listString += s;
            candList.remove(listString);         
        } 

正在为您制造问题，因为它仅适用于首次运行；对于其余 (n-1) 次运行，它不会删除任何内容！

我不明白您为什么要将候选名称加入 listString 变量？ 如果您需要删除单个候选名称，那么以下应该是正确的方法：

for (String s : loser) {
            //listString += s;
            candList.remove(s);         
        } 

有意义吗？

Answer 2

这是一个建议。不喜欢就离开吧！

解决此类问题的更清晰的方法是使用带有 候选人姓名将是关键，值是投票数。 当你遍历投票列表时，检查候选人的名字是否存在于地图中，如果存在，只需增加计数，否则将其设置为 1（这意味着你看到的第一个投票）

Answer 3

我认为您的代码有很多问题可能会导致问题。

for (String s : loser)
{
    listString += s;
    candList.remove(listString);
}

这段代码在失败者列表中添加每个名字，并试图将其从 candList 中删除，因此假设失败者列表中有 [joe, john, dave]，然后该循环说 remove("joe"),然后删除（“joejohn”）然后删除（“joejohndave”） 这真的是你想要的吗？

int votes = numFirstVotes(candidate, candidateList);

这里可能有问题，因为 ballotList 是全局的，也许你在这个函数中正确使用了它，但是因为我看不到我不知道的代码。

由于我们没有 numFirstVotes 的代码或 ballotList 的设置方式，因此很难同意您认为该代码有效。您的 cmets 不反映代码在做什么，应该删除或更新。

我认为真正的问题在这里

while (candList.size() > 2)

这就是说，循环直到列表中有 2 个或更少的项目。它不会说循环，直到列表中有 1 个或更少的项目，这基于你的 cmets 是你想要它做的。 因此，如果没有您的其余代码来测试我的猜测，我无法确定，但我认为您想将循环条件更改为

while (candList.size() >= 1)

如果更改后仍然无法正常工作，那么您的代码中可能还有更多问题，例如上面的 for 循环和 numFirstVotes 方法。

Answer 4

我会对你的代码做一些小的修改。您可以直接从该方法返回获胜者，而不是返回失败者并迭代地删除它们。基本上，您通过在每次迭代中删除最小元素来找到最大元素。这不是你应该接近的方式。

更改candidatesWithFewest方法candidatesWithHighest，并相应更改逻辑：

public ArrayList<String> candidatesWithHighest(ArrayList<String> candidateList) {
    ArrayList<String> winners = new ArrayList<String>(); //empty list for losers
    int maxTally = ballotList.size() + 1;      //number of min votes
    for (int can = 0; can < candidateList.size(); can++) {
        String candidate = candidateList.get(can);
        // // number of first place votes
        int votes = numFirstVotes(candidate, candidateList);
        if (votes > maxTally) {
            maxTally = votes;
            winners = new ArrayList<String>(); // Reset the list
        } else if (votes == maxTally) {
            winners.add(candidateList.get(can)); //adds winners with the same vote
        }
    }
    return winners;  // returns list of candidates with highest votes
}

然后你的第一个方法根本不需要任何while 循环。只需获取列表，检查大小。如果大于 1，则抛出错误：

public String getWinner(VoterBallots vbal, ArrayList<String> candList) {
    ArrayList<String> winners = vbal.candidatesWithHighest(candList);

    if (candList.size() < 2) { 
        return candList.iterator().next(); // Return the surviving candidate
    } else {
        return "Election is non decisive.";
    }
}

Answer 5

尝试使用candList.remove(s); 而不是candList.remove(listString);

另外，实际上在我看来，这种方法存在一些问题

public ArrayList<String> candidatesWithFewest(ArrayList<String> candidateList) {
    ArrayList<String> losers = new ArrayList<String>(); //empty list for losers
    int minTally = ballotList.size() + 1;      
    for (int can = 0; can < candidateList.size(); can++) {
        String candidate = candidateList.get(can);
        // // number of first place votes
        int votes = numFirstVotes(candidate, candidateList);
        if (votes < minTally) {
            minTally = votes; //.... here you have made minTally == votes
            losers = new ArrayList<String>(); // adds loser to list ..... here again you are repeating the first line of this method
        }
        if (votes == minTally) { //..... this will be true because although originally votes were less than minTally still, your assignment makes them equal
            losers.add(candidateList.get(can)); //adds losers with the same vote
        }
    }
    return losers;  // returns list of candidates with fewest votes
}