MergeSort

class Merge
{
    private static int[] aux;//定义一个数组用于存储归并时存储原数组
    public static void sort(int[] a)
    {
        aux = new int[a.length];//将数组aux的长度定义为与原数组的长度是一样的
        sort(a ,0, a.length-1);//将原数组进行划分
    }
    public static void sort(int[] a,int low,int high)
    {
        if (high<=low)//如果子数组中长度为1，此时就不再进行sort了
        {
            return;
        }
        int mid =low+ (high-low)/2;//定义一个中位数
        sort(a ,low,mid);//将a数组中的元素的前一半尽心再次sort
        sort(a ,mid+1,high);//将数组的后一半进行sort
        merge(a,low,mid,high);//将数组的前一半和后一半进行一个merge
    }
    public static void merge(int[] a,int low,int mid,int high)
    {
        int leftIndex = low;//定义前一半数组元素的Index
        int rightIndex = mid+1;//定义后一半元素的Index
        int tempIndex =low;//定义当前子数组的起始位置元素的Index
        for (int i =low;i<=high ;i++ )//将元素组a的元素复制到数组啊aux中
        {
            aux[i] = a[i];
        }
        while ((leftIndex<=mid)&&(rightIndex<=high))//实现归并
        {
            if (aux[leftIndex]<aux[rightIndex])
            {
                a[tempIndex] = aux[leftIndex];
                leftIndex++;
            }
            else 
            {
                a[tempIndex] = aux[rightIndex];
                rightIndex++;
            }
            tempIndex++;
        }
        if (leftIndex>mid)
        {
            for (;rightIndex<=high;rightIndex++,tempIndex++)
            {
                a[tempIndex] = aux[rightIndex];
            }
        }
        else
        {
            for (;leftIndex<=mid;leftIndex++,tempIndex++ )
            {
                a[tempIndex] = aux[leftIndex];
            }
        }
    }
    public static void printArr(int[] a)//输出数组
    {
        for (int i=0;i<a.length ;i++ )
        {
            if (i==0)
            {
                System.out.print("{"+a[i]+",");
            }
            else if (i<a.length-1)
            {
                System.out.print(a[i]+",");
            }
            else 
                System.out.println(a[i]+"}");
        }
    }
}
class MergeSort
{
    public static void main(String[] args)
    {
        int[] a = new int[]{3,44,38,5,47,15,36,26,27,2,46,4,19,50,48};
        int[] aux = new int[a.length];
        Merge.sort(a);
        Merge.printArr(a);
    }

}