Stacked Dozen

This is one of the new possible maps for Sokoban Level 2 in Hack'EM. It has 11 boulders and 10 holes, leaving 1 spare boulder. In the starting position, all the boulders are stacked on top of each other.

---------         ------  0 boulder
|.......|     ----|....-- ^ hole
|.......|    --..--.....| > starting position/downstairs
|...<...|  ---......-.|.| < upstairs
|.......|  |..........|.| + door
|.......|  |..0..-......|
|+------------.....--...|
|.^^^^^^^^^^^...|>......|
-------------------------

Strategy

First move the boulders from the stack to the position below. Then the boulders can be cleared as follows:

---------         ------   B u
|.......|     ----|....--  A l
|.......|    --..--.G...|  C dll
|...<...|  ---..D.EF-H|.|  A rddlll
|.......|  |..........|.|  B ldddllll
|.......|  |..AB.-.J.KL.|  D dlldddlllll
|+------------C...I--...|
|.^^^^^^^^^^^...|>......|
-------------------------

---------         ------   F u
|.......|     ----|....--  E llldddldllllll
|.......|    --..--.G...|  I uulllldddlllllll
|...<...|  ---....EF-H|.|  J lulllldddllllllll
|.......|  |..........|.|  F ddllllldddlllllllll
|.......|  |.....-.J.KL.|  G lddllllldddllllllllll
|+------------....I--...|
|.^^^^^^^^^^^...|>......|
-------------------------

---------         ------   H ullddllllldddlllllllllll
|.......|     ----|....--  K d
|.......|    --..--.....|  L llllulllldddllllllllllll
|...<...|  ---......-H|.|
|.......|  |..........|.|
|.......|  |.....-...KL.|
|+------------.....--...|
|.^^^^^^^^^^^...|>......|
-------------------------