如何使用比较器进行重复？

Question

我是 Java 的新手，我尝试制作一个比较器，将对象从 Min 排序到 Max，如果有重复项，会将它们发送到列表末尾以获得结果类似于 [1, 2, 3, 1, 2, 3, 1, 2, 3, 等等]。但即使是这个初始变体也不起作用！？我得到一个 ClassCastException，表明无法将 Integer 转换为 TestArr。哪里出错了？这是我的代码：

public class IntraArrayValuesComparison {
public static void main(String[] args) {
    ArrayList<Integer> num1 = new ArrayList<Integer>();     
        num1.add(40);
        num1.add(50);
        num1.add(50);
        num1.add(40);
        num1.add(20);
        num1.add(10);
        num1.add(10);
        num1.add(30);
        num1.add(20);
        num1.add(30);

    Collections.sort(num1, new ArraysValuesCompare());
    Iterator itr = num1.iterator();  
    while (itr.hasNext()) {  
        TestArr st = (TestArr)itr.next();  
        System.out.println(st.var);
        }
    System.out.println();
}
}

class TestArr {
int var;
TestArr (int var) {
    this.var = var;
}
}

class ArraysValuesCompare implements Comparator{
public int compare (Object o1, Object o2){
    TestArr a = (TestArr)o1;
    TestArr b = (TestArr)o2;
    if (a.var >= b.var)
        return 0;  
    else  
        return 1;  
        }
}

Answer 1

你不能用Comparator。

但是您可以对值进行排序，然后重新排列值，即重复将重复项移动到列表的末尾，就像您说的那样。

public static List<Integer> sortAscendingRepeated(Integer... values) {
    List<Integer> list = new ArrayList<>(Arrays.asList(values));
    Collections.sort(list);
    for (int i = 1; i < list.size(); i++)
        if (list.get(i).equals(list.get(i - 1)))
            list.add(list.remove(i--));
    return list;
}

测试

System.out.println(sortAscendingRepeated(40, 50, 50, 40, 20, 10, 10, 30, 20, 30));
System.out.println(sortAscendingRepeated(1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 5, 4));

输出

[10, 20, 30, 40, 50, 10, 20, 30, 40, 50]
[1, 2, 3, 4, 5, 1, 2, 3, 4, 1, 2, 3]

Answer 2

直方图可以用来合并统计。

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

public class IntraArrayValuesComparison {

    private static void sort(List<TestArr> num1) {
        Map<TestArr, Integer> histogram = new TreeMap<TestArr, Integer>();
        for(TestArr test : num1) {
            Integer count = histogram.get(test);
            if(count == null)
                count = 0;
            histogram.put(test, ++count);
        }

        num1.clear();
        while(!histogram.isEmpty()) {
            Iterator<TestArr> itr = histogram.keySet().iterator();  
            while (itr.hasNext()) {  
                TestArr st = itr.next(); 
                Integer count = histogram.get(st);
                if(count > 0) {
                    num1.add(st);
                    histogram.put(st, --count);
                    continue;
                }
                itr.remove();
            }
        }
    }

    public static void main(String[] args) {
        List<TestArr> num1 = new ArrayList<>();     
        num1.add(new TestArr(40));
        num1.add(new TestArr(50));
        num1.add(new TestArr(50));
        num1.add(new TestArr(40));
        num1.add(new TestArr(20));
        num1.add(new TestArr(10));
        num1.add(new TestArr(10));
        num1.add(new TestArr(30));
        num1.add(new TestArr(20));
        num1.add(new TestArr(30));

        sort(num1);

        Iterator<TestArr> itr = num1.iterator();  
        while (itr.hasNext()) {  
            TestArr st = itr.next();  
            System.out.println(st.var);
        }
        System.out.println();
    }

}

class TestArr implements Comparable<TestArr> {
    Integer var;
    TestArr (int var) {
        this.var = var;
    }

    @Override
    public int compareTo(TestArr o) {
        if(o == null)
            return -1;
        return var.compareTo(o.var);
    }

}

Answer 3

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.TreeMap;

public class IntraArrayValuesComparison {
    private static boolean isInRange(Integer st, Integer val) {
        final int DELTA = 5;
        return val.intValue() >= (st.intValue() - DELTA) && val.intValue() <= (st.intValue() + DELTA);
    }

    private static List<Integer> getDeckWithLessCards(List<List<Integer> > resultDecks) {
        if(resultDecks.isEmpty())
            return new ArrayList<>();

        List<Integer> cards = resultDecks.get(0);
        for(int i= 1; i < resultDecks.size(); ++i) {
            if(resultDecks.get(i).size() < cards.size())
                cards = resultDecks.get(i);
        }
        return cards;
    }

    private static Collection<List<Integer> > sort(List<Integer> deck, Integer splitSize) {
        Map<Integer, List<Integer>> decks = new TreeMap<>();
        outerLoop:
        for(Integer card : deck) {
            List<Integer> cards = new ArrayList<>();
            Iterator<Integer> itr = decks.keySet().iterator();  
            while (itr.hasNext()) {
                Integer masterCard = itr.next(); 
                if(isInRange(card, masterCard)) {                   
                    decks.get(masterCard).add(card);
                    continue outerLoop;
                }
            }
            decks.put(card, cards);
            decks.get(card).add(card);
        }

        System.out.println("Arranged decks:\t" + decks.values());
        //do transpose
        List<List<Integer> > resultDecks = new ArrayList<>();
        if(splitSize == null || splitSize < 2)
            splitSize = decks.size();
        for(int i= 0; i < splitSize; ++i)
            resultDecks.add(new ArrayList<>());

        boolean lastCard = false;
        while(!decks.isEmpty()) {
            Iterator<Integer> itr = decks.keySet().iterator(); 
            if (itr.hasNext()) {
                Integer masterCard = itr.next(); 
                List<Integer> cards = decks.get(masterCard);
                Integer card = Collections.min(cards);
                cards.remove(card);
                boolean uno = cards.isEmpty();
                if(uno) {
                    lastCard = true;
                    getDeckWithLessCards(resultDecks).add(card);
                    itr.remove();
                }               
                else if(lastCard) {
                    resultDecks.get(0).add(card);
                    lastCard = false;
                }
                else
                    getDeckWithLessCards(resultDecks).add(card);
            }           
        }
        return resultDecks;
    }

    public static void main(String[] args) {
        String[] data = null;
        System.out.print("Please input data (1, 5, 10, 2, 15, 3, 20): ");
        try (Scanner scanner = new Scanner(System.in)) {
            data = scanner.nextLine().split(",");
        } catch(Exception ex) {
            System.out.println("\nIncorrect data format.");
            return;
        }

        if(data == null || data.length < 2) {
            System.out.println("Incorrect data format.");
            return;
        }

        List<Integer> deck = new ArrayList<>();  
        for(String value : data)
            deck.add(new Integer(value.trim()));

        Collection<List<Integer> > resultDecks = sort(deck, 3);
        System.out.println("Final decks:\t" + resultDecks);

        System.out.println();
    }

}

如何使用比较器进行重复？

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