Question

I do have int pairs, i.e; (int ,int)

1) Given k such pairs, check if they are unique. i.e; size of the Set formed using k pairs is k ?
2) if the given k records are unique then store them in sorted order ( by x and resolve conflict by y)
3) Given n such sets of size k, create a set of sets.

Example of requirement 1 and 2
if k = 3

(100, 100) (110, 300) (120, 200) is a valid set and in sorted order.
(100, 100) (300, 200) (200, 300) is a valid set but not in sorted order.
(100, 100) (100, 200) (100, 200) is in valid set

Example of requirement 3
input:

(100, 100) (200, 300) (300, 200)
(100, 100) (200, 300) (300, 200)
(100, 100) (201, 300) (300, 200)

output:

(100, 100) (200, 300) (300, 200)
(100, 100) (201, 300) (300, 200)

This is the closest analogy to the real problem i am facing. I need to get this done in Java and i have never worked in java. I am a intermediate c++ programmer.

I could solve 1 and 2 via some ugly coding and sorting.
However i am not able to get 3. Below is what i could get so far for 3. The class pair implements comparable

(poc code)

import java.util.HashSet;
public class set {
    public static void main (String []args) {
        HashSet<Pair> s1 = new HashSet();
        s1.add(new Pair(10,10));
        s1.add(new Pair(10,10));

        HashSet<Pair> s2 = new HashSet();
        s2.add(new Pair(10,10));
        s2.add(new Pair(10,10));

        HashSet<HashSet<Pair>> s12 = new HashSet();
        s12.add(s1);s12.add(s2);
        for ( HashSet<Pair> hs : s12) {
            for (Pair p :  hs) {
                System.out.println(""+ p.toString());
            }
        }
    }
}

Answer 1

Looks like you didn’t override equals and/or hashCode methods in Pair class.

For example if your Pair class has the following structure :

protected K value1;
protected V value2; 

You should implement equals and hashCode as(example) :

 public boolean equals(Object obj) {
    if (!(obj instanceof Pair))
        return false;
    Pair that = (Pair)obj;
    boolean result = true;
    if (this.getValue1() != null)
        result = this.getValue1().equals(that.getValue1());
    else if (that.getValue1() != null)
        result = that.getValue1().equals(this.getValue1());

    if (this.getValue2() != null)
        result = result && this.getValue2().equals(that.getValue2());
    else if (that.getValue2() != null)
        result = result && that.getValue2().equals(this.getValue2());

    return result;
} 


public int hashCode() {
    int result = value1 != null ? value1.hashCode() : 0;
    result = 31 * result + (value2 != null ? value2.hashCode() : 0);
    return result;
}