归并排序(java)

分组

操作数量级减少

//临时数组  以空间换时间
private static int[] assist;
//数据数组
private static int[] datas;

//初始化数据
datas = new int[]{4, 3, 2, 10, 12, 1, 5, 6, 11, 7};
System.out.println("原始数据:"+ Arrays.toString(datas));

//开始排序
sort(datas);
System.out.println(Arrays.toString(datas));

 //归并排序
    public static void sort(int[] array){
        assist = new int[array.length];
        sort(array, 0, array.length-1);
    }

    //递归分组
    public static void sort(int[] array, int di, int hi){
        if (hi <= di){
            return;
        }
        int mid = di+(hi-di)/2;
        sort(array,di, mid);
        sort(array, mid+1,hi);
        mergin(array, di, mid, hi);
    }

 //分组合并
    public static void mergin(int[] array, int di, int mid, int hi){
        int i=di;
        int j = mid+1;
        for (int n=di;n<=hi;n++){
            if (i <= mid && j <= hi){
                if (array[i] < array[j]){
                    assist[n] = array[i];
                    i+=1;
                }else{
                    assist[n] = array[j];
                    j+=1;
                }
                continue;
            }
            if(i<=mid){
                assist[n] = array[i];
                i+=1;
                continue;
            }
            if(j<=hi) {
                assist[n] = array[j];
                j += 1;
                continue;
            }
        }
//将临时数组中的数据移动到数据数组中
        for (int n=di;n<=hi;n++) {
            datas[n] = assist[n];
        }
    }

组内排序