package ch5;

import java.util.Iterator;
import java.util.TreeSet;

public class MathArrays {

    /**
     * Returns an array consisting of the unique values in {@code data}.
     * The return array is sorted in descending order.  Empty arrays
     * are allowed, but null arrays result in NullPointerException.
     * Infinities are allowed.  NaN values are allowed with maximum
     * sort order - i.e., if there are NaN values in {@code data},
     * {@code Double.NaN} will be the first element of the output array,
     * even if the array also contains {@code Double.POSITIVE_INFINITY}.
     *
     * @param data array to scan
     * @return descending list of values included in the input array
     * @throws NullPointerException if data is null
     * @since 3.6
     */
    public static int[] unique(int[] data) {
        TreeSet<Integer> values = new TreeSet<Integer>();
        for (int i = 0; i < data.length; i++) {
            values.add(data[i]);
        }
        final int count = values.size();
        final int[] out = new int[count];
        Iterator<Integer> iterator = values.iterator();
        int i = 0;
        while (iterator.hasNext()) {
            out[count - ++i] = iterator.next();
        }
        return out;
    }

}