currency permutation - java - TUM homework

    /**
     * Counts the number of possibilities to get a total value of exactly {@code max} using
     * only the values given in {@code remainingCoins}.
     * @param sum the accumulated value
     * @param max the maximum value
     * @param remainingCoins a list of coins
     * @return the number of possibilities
     */
    static int numPossibilities(int sum, int max, List<Integer> remainingCoins) {
        /* Implementation
         * Copyright (c) 2014  Niklas Rosenstein
         *
         * Permission is hereby granted, free of charge, to any person obtaining a copy
         * of this software and associated documentation files (the "Software"), to deal
         * in the Software without restriction, including without limitation the rights
         * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
         * copies of the Software, and to permit persons to whom the Software is
         * furnished to do so, subject to the following conditions:
         *
         * The above copyright notice and this permission notice shall be included in
         * all copies or substantial portions of the Software.
         *
         * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
         * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
         * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
         * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
         * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
         * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
         * THE SOFTWARE. */

        if (sum > max)
            return 0;
        else if (sum == max)
            return 1;

        int result = 0;
        List<Integer> current = remainingCoins;
        while (current != null) {
            result += numPossibilities(sum + current.head, max, current);
            current = current.tail;
        }

        return result;
    }