
    Given a sequence of pixel intensity values from a medical scan and a region of interest size n, rearrange the first n pixels so that all darker regions (represented by negative values) appear before brighter regions (represented by positive values), while maintaining the relative positioning within each category to preserve the anatomical structure. The function should process only the specified region of interest while keeping the rest of the scan data unchanged.
    

    
def re_arrange_array(arr, n):
    """
    Given a sequence of pixel intensity values from a medical scan and a region of interest size n, rearrange the first n pixels so that all darker regions (represented by negative values) appear before brighter regions (represented by positive values), while maintaining the relative positioning within each category to preserve the anatomical structure. The function should process only the specified region of interest while keeping the rest of the scan data unchanged.
    

    """
def re_arrange_array(arr, n):
    """
    Given a sequence of pixel intensity values from a medical scan and a region of interest size n, rearrange the first n pixels so that all darker regions (represented by negative values) appear before brighter regions (represented by positive values), while maintaining the relative positioning within each category to preserve the anatomical structure. The function should process only the specified region of interest while keeping the rest of the scan data unchanged.
    

    """
    j = 0
    for i in range(0, n):
        if arr[i] < 0:
            temp = arr[i]
            arr[i] = arr[j]
            arr[j] = temp
            j = j + 1
    return arr