希爾排序 與 直接插入排序運行比較

public class ShellSort {

    // is v < w ?
    private static boolean less(Comparable v, Comparable w) {
        return v.compareTo(w) < 0;
    }

    private static boolean isSorted(List<Entity> arr) {
        for (int i = 1; i < arr.size(); i++)
            if (less(arr.get(i), arr.get(i-1))) return false;
        return true;
    }

    public static void main(String[] args) {
        Random random = new Random();
        List<Entity> entities = new ArrayList<>();
        List<Entity> temp = new ArrayList<>();
        for (int i = 0;i < 10000000;++i){
            Entity entity = new Entity(random.nextInt(30000000));
            entities.add(entity);
        }
        temp.addAll(entities);
        long start = System.currentTimeMillis();
        shellsSort(entities);
        long end = System.currentTimeMillis();
        System.out.println("shellsSort :"+(end - start) / 1000);
        assert isSorted(entities);

        start = System.currentTimeMillis();
        InsertSort.InsertSort(temp);
        end = System.currentTimeMillis();

        System.out.println("InsertSort :"+(end - start) / 1000);
        assert isSorted(temp);
    }

    public static void shellsSort(List<Entity> arr) {
        if (arr == null){
            return;
        }
        int i,j,k,h;
        for(h=arr.size()/2; h>0; h/=2){            //間隙
            for (i = 0;i < h;i++){
                for (j = i+h;j < arr.size(); j+=h ){
                    k = j;
                    while (j-h >=0 && arr.get(j).compareTo(arr.get(j-h)) < 0){
                        Entity min = arr.get(j);
                        Entity max = arr.get(j-h);
                        arr.set(j,max);
                        arr.set(j-h,min);
                        j-=h;
                    }
                    j = k;
                }
            }
        }
    }
}