css3 - flex layout at both ends

Question

There is such a requirement. Boxes 1, 2, and 3 need to be centered on the left, top and bottom, and boxes 4, 5, and 6 need to be centered on the right, top and bottom.
Is it possible to use flex layout? After checking some information, it seems that it is not possible.

Only the following common situations can be realized:

Answer 1

Why is it so rigid...
First form 1 2 3组成一个整体，放在左边；4 5 6 into a whole and place it on the right side.

Then just use these two layouts separately...flex