public int partition(int[] src,int st,int et)
    {
       int left = st;
       int right = et;
       int pivot = src[(st + et)/2];
       while(left<=right)
       {
           while(src[left]<pivot) left++;
           while(src[right]>pivot) right--;
           if(left <= right)
           {
               if(left != right)
                swap(src,left,right);
               left++;
               right--;
           }
       }
       return left;
    }