在2的Java循环中从2的ArrayList中删除元素

Question

There are N boys and N girls. Only a boy and a girl can form a dancing pair (ie no same sex dancing pairs are allowed). The only other condition in making pairs is that their absolute difference in height should be less than or equal to K.

Find the maximum number of pairs that can be formed so that everyone has a unique partner.

Input Format The first line will contain two integers, N and K. The second line will contain N integers, the heights of N boys. The third line will contain N integers, the heights of N girls.

Constraints 1≤N≤105 1≤K≤109 1≤height of boy or girl≤109

Output Format A single line containing the maximum number of possible pairs.

My problem is in deleting the elements from the tow arrays after satisfying the condition. (after storing the 2 arrays)

The first algorithm i used :

Arrays.sort(ArrBoys);
    Arrays.sort(ArrGirls);
    double count = 0;
    for (int i = 0; i < ArrGirls.length; i++) {
        for (int j = 0; j < ArrBoys.length; j++) {
            if ((int) Math.abs(ArrBoys[j] - ArrGirls[i]) <= k) {
                ArrBoys[j] = 0;
                ArrGirls[i] = 0;
                count++;
                break;
            }
        }
    }
    System.out.println((int) count);

and this is definitely wrong, because we need to delete that elements not to make them zeros, So i realized that i need to convert them to ArrayLists. then i came with this code :

double count = 0;
    int dif = 0;
    for (Integer ArrGirl : ArrGirls) {
        loop1:
        {
            for (Integer ArrBoy : ArrBoys) {
                dif = (int) Math.abs(ArrBoy - ArrGirl);
                if (dif <= k) {
                    System.out.println("we took " + ArrBoy + " from boys with "
                    + ArrGirl + " from girls, thier dif is " + dif);
                    ArrBoys.remove(ArrBoy);
                    ArrGirls.remove(ArrGirl);
                    count++;
                    break loop1;
                }
            }
        }
    }
    System.out.println((int) count);

using this algorithm gives me an exception like this :

Exception in thread "main" java.util.ConcurrentModificationException at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) at java.util.ArrayList$Itr.next(ArrayList.java:851)

after i searched about this exception i found that i should use Iterator while using remove method, then i used this code :

double count = 0;
    int dif = 0;
    Iterator<Integer> iteB = ArrGirls.iterator();
    Iterator<Integer> iteG = ArrGirls.iterator();
    while (iteG.hasNext()) {
        int value2 = iteG.next();
        while (iteB.hasNext()) {
            int value = iteB.next();
            dif = (int) Math.abs(value - value2);
            if (dif <= k) {
                System.out.println("we took " + value + " from boys with " + value2
                        + " from girls, thier dif is " + dif);
                count++;
                iteB.remove();
                iteG.remove();

            }
        }
    }
    System.out.println((int) count);

this code gives me wrong information and also gives me the same exception.

This is the first time i use ArrayList, do you have any idea to correct this code?

Answer 1

You have to reassign the iterator for girls everytime.And this works fine

 int k = 5;
    int count = 0;
    ArrayList<Integer> ArrGirls = new ArrayList<>((List<Integer>) Arrays.asList(new Integer[]{34, 37, 28, 16, 44, 36, 37, 43, 50, 22}));
    ArrayList<Integer> ArrBoys = new ArrayList<>((List<Integer>) Arrays.asList(new Integer[]{13, 28, 41, 10, 14, 27, 41, 27, 23, 37}));
    for (Iterator<Integer> iteG = ArrGirls.iterator(); iteG.hasNext();) {
        {
            Integer ArrGirl = iteG.next();
            for (Iterator<Integer> iteB = ArrBoys.iterator(); iteB.hasNext();) {
                Integer ArrBoy = iteB.next();
                int dif = (int) Math.abs(ArrBoy - ArrGirl);
                if (dif <= k) {
                    System.out.println("we took " + ArrBoy + " from boys with "
                            + ArrGirl + " from girls, thier dif is " + dif);
                    ArrBoys.remove(ArrBoy);
                    ArrGirls.remove(ArrGirl);
                    iteG = ArrGirls.iterator();//You have to reset the value of iterationGirls
                    count++;
                    break;
                }
            }
        }
    }
    System.out.println(count);

Answer 2

// This helps I guess with little modifications for taking the inputs
public class Boy {

    private int height;

    public int getHeight() {
        return height;
    }

    public void setHeight(int height) {
        this.height = height;
    }

}

public class Girl {

    private int height;

    public int getHeight() {
        return height;
    }

    public void setHeight(int height) {
        this.height = height;
    }

}

import java.util.ArrayList;
import java.util.List;
import java.util.Random;


public class Program {

    public static void main(String[] args) {
        int k=11;
        Random random = new Random();
        List<Boy> boys = new ArrayList<Boy>();
        List<Girl> girls = new ArrayList<Girl>();
        int noOfcombinations = 0;
        for(int i=1;i<=100;i++)
        {
            Boy boy = new Boy();
            boy.setHeight(random.nextInt(109));
            Girl girl = new Girl();
            girl.setHeight(random.nextInt(109));
            boys.add(boy);
            girls.add(girl);
        }
        for (Boy boy : boys) {
            for (Girl girl : girls) {
                if(Math.abs(boy.getHeight()-girl.getHeight())<k)
                {
                    noOfcombinations++;
                }

            }
        }
        System.out.println("No of combinations is "+noOfcombinations);

    }

}