快速排序

private static List<Integer> quicksort(List<Integer> list) {
    if (list.size() < 2) { // 基线条件：为空或只包含一个元素的数组是“有序”的
        // base case, arrays with 0 or 1 element are already "sorted"
        return list;
    } else {
        // recursive case
        // 递归条件
        Integer pivot = list.get(0);

        // sub-array of all the elements less than the pivot
        // 由所有小于基准值的元素组成的子数组
        List<Integer> less = list.stream().skip(1).filter(el -> el <= pivot).collect(Collectors.toList());

        // sub-array of all the elements greater than the pivot
        // 由所有大于基准值的元素组成的子数组
        List<Integer> greater = list.stream().skip(1).filter(el -> el > pivot).collect(Collectors.toList());

        return Stream.of(quicksort(less).stream(), Stream.of(pivot), quicksort(greater).stream())
                .flatMap(Function.identity()).collect(Collectors.toList());
    }
}

public static void main(String[] args) {
    System.out.println(quicksort(Arrays.asList(10, 5, 2, 3))); // [2, 3, 5, 10]
}