# 16 Step Switchover

The picture above shows two arrangements of four rectangular blocks, each labelled A to D. The arrangement on the left is the starting arrangement, the one on the right is the goal position. To solve this puzzle you need to slide the blocks around so that the starting arrangement is transformed into the goal arrangement.

Oh, but there's a catch...

You need to solve the puzzle in 16 moves or under.

A move consists of moving a block to a new position so long as you don't hop a block over another block, twist a block around on the spot, move a block on top of another block, or move a block out of the frame.

Good luck!

• I can do it in one move: rotate the puzzle 180 degrees. (Of course that's cheating.) Sep 19 '21 at 23:17
• @MackTuesday Well done! Sep 20 '21 at 2:53
• Is it allowed to push a piece by moving another piece and does this count as 1 move or 2? Sep 20 '21 at 10:17

I think this works:

. B . .  0
. B C C
A A D .
. . D .

. B . .  1
. B C C
. . D .
A A D .

. . . .  2
. B C C
. B D .
A A D .

C C . .  3
. B . .
. B D .
A A D .

C C . D  4
. B . D
. B . .
A A . .

C C . D  5
. . . D
. . . B
A A . B

C C . .  6
. . . .
. . D B
A A D B

C C A A  7
. . . .
. . D B
. . D B

. . A A  8
. . . .
. . D B
C C D B

. D A A  9
. D . .
. . . B
C C . B

. D A A  10
. D . .
C C . B
. . . B

. D . .  11
. D A A
C C . B
. . . B

. D . .  12
. D A A
C C B .
. . B .

• I was happy when I just managed to get it in 16 :P Sep 18 '21 at 15:11

Took me some time, but I got 13 steps:

• I guess you can combine the two consecutive orange steps 3 and 4 to save a step. Sep 18 '21 at 16:52
• This is 12 moves, not 13, right? Sep 19 '21 at 18:23
• @OldBunny2800 13, originally thought it was 14 for the same reason. Sep 19 '21 at 18:54
• I count 12 - moves 3 and 4 are actually just one move. Sep 19 '21 at 19:02
• Ohhhh good eye lol 😂 Sep 19 '21 at 19:13