Sparse set

import java.util.*;

public class IntSparseSet extends AbstractSet<Integer>{
    private int[] sparse;
    private int[] dense;
    private int n, low, high;

    public IntSparseSet(int low, int high){
        sparse = new int[high];
        dense = new int[high];
        n = 0;
        this.low = low;
        this.high = high;
    }

    public boolean contains(Integer x){
        return (sparse[x] >=0 &&
            sparse[x] < n &&
            dense[sparse[x]] == x);
    }

    public int size(){
        return n;
    }

    public boolean add(Integer x){
        if (x < low || x >= high){
            return false;
        }
        if (contains(x)) return false;
        dense[n] = x;
        sparse[x] = n;
        n++;
        return true;
    }

    public boolean remove(Integer x){
        if (!contains(x)) return false;
        int temp = dense[n - 1];
        dense[sparse[x]] = temp;
        sparse[temp] = sparse[x];
        n--;
        return true;
    }

    public void clear(){
        n = 0;
        //return true;
    }

    public Iterator<Integer> iterator(){
        return new SparseIterator();
    }

    private class SparseIterator implements Iterator<Integer>{
        private int pos;

        public SparseIterator(){
            pos = 0;
        }

        public boolean hasNext() { return pos < n; }
        public Integer next() { return dense[pos++]; }
    }
}