排序java ArrayList合并排序

Question

当我运行这个程序时，合并排序没有发生，我也不知道问题出在哪里。int-brelem和SortThread任务参数之所以存在，只是因为我需要它们正确地重写父类的方法，以便它们在这种情况下不起任何作用

class MergeSort extends Sort {

@Override
ArrayList sort(ArrayList<Integer> a, int brelem, SortThread task) {
    if (a.size() > 1) {

        ArrayList<Integer> firstHalf = new ArrayList<>(a.subList(0, a.size() / 2));

        firstHalf.subList(0, a.size() / 2);
        firstHalf=sort(firstHalf, a.size() / 2, task);

        ArrayList<Integer> secondHalf = new ArrayList<>(a.subList(a.size()/2, a.size()));

        secondHalf=sort(secondHalf, secondHalf.size(), task);

        ArrayList<Integer> temp = merge(firstHalf, secondHalf);
        a.subList(0, temp.size());
    }
    return a;
}

private static ArrayList merge(ArrayList<Integer> list1, ArrayList<Integer> list2) {
    ArrayList<Integer> temp = new ArrayList<>();

    int current1 = 0;
    int current2 = 0;
    int current3 = 0;

    while (current1 < list1.size() && current2 < list2.size()) {
        if (list1.get(current1) < list2.get(current2)) {
            temp.set((current3++), list1.get(current1++));
        } else {
            temp.set((current3++), list2.get(current2++));
        }
    }

    while (current1 < list1.size()) {
        temp.set((current3++), list1.get(current1++));
    }

    while (current2 < list2.size()) {
        temp.set((current3++), list2.get(current2++));
    }

    return temp;
}

}

Answer 1

除此之外，您返回的是a，而不是temp。据我所知，你从不修改a

也许你对List.subList()的功能感到困惑。它返回列表的视图，因此无论您在sort的倒数第二个语句中使用它做什么，都将无效，因为您忽略了返回值