void quicksort(int *a,int left,int right){

    if(left >= right){

        return ;

    }

    int i = left;

    int j = right;

    int key = a[left];

    while(i < j)

    {

        while(i < j && key <= a[j]){

            j--;

        }

        a[i] = a[j];

        while(i < j && key >= a[i]){

            i++;

        }

        a[j] = a[i];

    }

    a[i] = key;

    quicksort(a, left, i - );

    quicksort(a, i + , right);

}