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Datastructures and utility classes for non-negative integers

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/*
 * Copyright (C) 2017 Tobias Meggendorfer
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */

package de.tum.in.naturals.set;

import it.unimi.dsi.fastutil.ints.IntIterator;
import java.util.NoSuchElementException;

/**
 * An iterator which yields all integers in {@code [from, to)} in descending order.
 */
public class ReverseRangeIterator implements IntIterator {
    private final int from;
    private int current;

    public ReverseRangeIterator(int from, int to) {
        if (to < from) {
            throw new IllegalArgumentException("To must be larger or equal than from");
        }
        this.from = from;
        current = to - 1;
    }

    @Override
    public boolean hasNext() {
        return current >= from;
    }

    @Override
    public int skip(int n) {
        int pos = current - n;
        if (pos >= from) {
            current = pos;
            return n;
        }
        int result = current - from + 1;
        current = from - 1;
        return result;
    }

    @Override
    public int nextInt() {
        if (current < from) {
            throw new NoSuchElementException();
        }
        int result = current;
        current -= 1;
        return result;
    }
}