CareerCup

Another difference apart from what @RV mentioned -
1) A hash function takes an input and provides a short unique representation of the input. Anyone who has access to the hash function can get the same output for the given input.
However, an encryption function needs a secret key to get the output.

2) The purpose of hashing is to get integrity of data. The purpose of encryption is to get confidentiality.

Set is an interface. How did you create a new instance on this line -

Set<Integer>[] allSets = new Set[a.length];

import java.util.ArrayList;

public class Stack 
{
	private ArrayList<Integer> stack;
	
	public Stack()
	{
		stack = new ArrayList<Integer>();
	}
	
	public int push (int value)
	{
		stack.add(value);
		return stack.size() - 1;
	}
	
	public int pop ()
	{
		int value = stack.get(stack.size() - 1);
		stack.remove(stack.size() - 1);
		return value;
	}
	
	public int getMiddle ()
	{
		return stack.get(stack.size()/2);
	}
	
	public int deleteMiddle ()
	{
		int value = stack.get(stack.size()/2);
		stack.remove(stack.size()/2);
		return value;
	}
}

For the sake of brevity, the middle element is the 3 when there are 6 elements in the ArrayList. i.e [0,1,2,3,4,5]