Question

I want to implement the union, intersect, difference and reverse operations in Java.

First I have 2 instances of ArrayList<Integer>

a = [0,2,4,5,6,8,10]
b = [5,6,7,8,9,10]

a union b should return c = [0,2,4,5,6,7,8,9,10]

a intersect b should return c = [5,8,10]

a difference b should return c = [0,2,4]

reverse a = [10,8,6,5,4,2,0]

Something like this.

How to implement that method in Java?

---

Note that I have to start with the following template:

package IntSet;
import java.util.ArrayList;
import java.util.Collection;


public class IntSet {
    
    private ArrayList<Integer> intset;
    
    public IntSet(){
        intset = new ArrayList<Integer>();
    }
    
    public void insert(int x){
        intset.add(x);
    }
    
    public void remove(int x){
        //implement here
        intset.indexOf(x);
    }
    
    public boolean member(int x){
        //implement here
        return true;
    }
    
    public IntSet intersect(IntSet a){
        //implement here
        return a;
    }
    
    public IntSet union(IntSet a){
        //implement here
        return a;
    }
    
    public IntSet difference(IntSet a){
        //implement here
        IntSet b = new IntSet();
        return b; 
    }
}

Answer 1

//Union 
List<Integer> c = new ArrayList<Integer>(a.size() + b.size());
addNoDups(c,a);
addNoDups(c,b);

private void addNoDups(List<Integer> toAddTo,List<Integer> iterateOver) {
    for(Integer num:iterateOver){
        if(toAddTo.indexOf(num) == -1) {
            toAddTo.add(num);
        }
    }
}

//intersection
List<Integer> c = new ArrayList<Integer> (a.size() > b.size() ?a.size():b.size());
c.addAll(a);
c.retainAll(b);

//difference a-b
List<Integer> c = new ArrayList<Integer> (a.size());
c.addAll(a);
c.removeAll(b);