java - 如何将公共(public)元素组合到一个数组中？

Question

我正在尝试将三个数组合并为一个数组。只保留共同的元素。这不是一个重复的问题。我知道网上还有其他示例，但那是使用 int []，我不知道如何使用 Comparable。

我需要什么帮助:

1. 如何将单个组合/更新数组添加到二维数组。

2. 如何计算元素每次比较的迭代次数。

3. 如果我想要如何将我现在拥有的数组更改为列表？ - 我在想也许添加起来会更容易。

我是编程新手，非常感谢您的帮助。我正在尝试通过阅读书籍和在线搜索来学习 java。

这就是我目前所拥有的。

public class Common{

Comparable [] col_1 = {1, 1, 2};
Comparable [] col_2 = {1, 1, 2,3};
Comparable [] col_3= {1, 1, 2,3,4,};
Comparable [][] collections = {col_1, col_2, col_3};
int comparisonCount = 0


public Comparable[] findCommon(Comparable [][] collections){

int i, j, k, x, y;

for(i = 0; i< col_1.length; i++){
    for(j = 0; j < col_2.length; j++){
        for(k = 0; k < col_3.length; k++){

comparisonCount++;     
// This should be counting but is not...

if(col_1[i].compareTo(col_2[j]) == 0 && col_1[i].compareTo(col_3[k]) ==0){

//keep searching until last element & allow duplicates & add to collections or a temp[]


                }
        }
    }
}

// Here I'm not sure how to add the elements to the collection


for (x = 0; x < collections.length; x++){
    for(y = 0; y< collections[x].length; y++){
        collections [x][y] = ?????? // not sure how to add results here
        }
    }
}


public void setComparisons(int count){
    count = comparisonCount;
}



public int getComparisons(){

    return comparisonCount;
}



public class Sorting {

public static void main(String[] args) {

    Common m = new Common();
    //I want to test it from here but I don't know how to initialize each array.        

    for(int x=0; x < m.collections.length; x++){
        for(int y= 0; y< m.collections[x].length; y++){
        System.out.println(m.collections[x][y]);
    }
// what I should be getting is only (1, 1, 2) -  the order is not important really. I just want to learn. 

    }
    System.out.println(m.getComparisons());

}

Answer 1

要仅保留可比较集中的公共(public)元素，您可以使用 TreeSet，它使用传递的比较器比较元素。

此外，使用自定义比较器，您可以计算元素相互比较的次数:

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.TreeSet;

public class Main {
    public static Comparable[] findCommon(Comparable[][] collections, Comparator comparator) {
        TreeSet<Comparable> set = new TreeSet<Comparable>(comparator);
        Collections.addAll(set, collections[0]);

        for (int i = 1; i < collections.length; i++)
            set.retainAll(Arrays.asList(collections[i]));

        return set.toArray(new Comparable[set.size()]);
    }

    public static void main(String[] args) {
        Comparable[] col_1 = {1, 1, 2};
        Comparable[] col_2 = {1, 1, 2, 3};
        Comparable[] col_3 = {1, 1, 2, 3, 4};

        Comparable[][] collections = {col_1, col_2, col_3};
        final int comparisonCount = 0;

        CountingComparator comparator = new CountingComparator();
        System.out.println(Arrays.toString(findCommon(collections, comparator)));
        System.out.println(comparator.getComparisonCount());
    }

    private static class CountingComparator implements Comparator<Comparable> {
        private int comparisonCount;

        public int getComparisonCount() {
            return comparisonCount;
        }

        @Override
        public int compare(Comparable o1, Comparable o2) {
            comparisonCount++;
            return o1.compareTo(o2);
        }
    }
}