Sokoban Level 4a

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This is one of the last levels of Sokoban. Behind the holes is a treasure zoo with a prize behind one of the three doors. There are 18 boulders and 16 holes. In NetHack 3.4.3 and variants based on it, the prize is a bag of holding. In NetHack 3.6.0 and variants based on it, the prize may be a bag of holding or an amulet of reflection, with equal probability. Except the storage area, it is the same as Level 23 in the 1984 Thinking Rabbit Sokoban game.

0 boulder
^ hole
@ starting position/downstairs
< upstairs
--------------------------
|@......^^^^^^^^^^^^^^^^.|
|.......----------------.|
-------.------         |.|
 |...........|         |.|
 |.0.0.0.0.0.|         |.|
--------.----|         |.|
|...0.0..0.0.|         |.|
|...0........|         |.|
-----.--------   ------|.|
 |..0.0.0...|  --|.....|.|
 |.....0....|  |.+.....|.|
 |.0.0...0.--  |-|.....|.|
-------.----   |.+.....+.|
|..0.....|     |-|.....|--
|........|     |.+.....|
|...------     --|.....|
-----            -------

Strategy

The following solution solves the level without putting any boulders in an immobile position. You can watch this solution as a ttyrec video. Faster solutions which do not necessarily leave every boulder free might exist.

All boulders are replaced by letters so they can be referred to. Moving the boulders is shortened to r for right, l for left, u for up, d for down. An asterisk is used to denote the last move filled a hole (and thus removed the boulder from the game). So Nddrr* means move boulder N two times down and two times to the right into a hole.

Store some boulders of the 3rd room in the 4th and make some way:

-------------------------- K l
|@......^^^^^^^^^^^^^^^^.| N rrr
|.......----------------.| R rrr
-------.------         |.| P rrdd dlll lur 
 |...........|         |.| F ll
 |.A.B.C.D.E.|         |.| J rddd drrd ddll lllu
--------.----|         |.|
|...F.G..H.I.|         |.|
|...J........|         |.|
-----.--------   ------|.|
 |..K.L.M...|  --|.....|.|
 |.....N....|  |.+.....|.|
 |.O.P...Q.--  |-|.....|.|
-------.----   |.+.....+.|
|..R.....|     |-|.....|--
|........|     |.+.....|
|...------     --|.....|
-----            -------

Push G and H out of the way so you can move some of the boulders of the 1st room to the 3rd and 4th room:

-------------------------- G ll
|@......^^^^^^^^^^^^^^^^.| H ll
|.......----------------.| D lddd llld dddr
-------.------         |.| C rddd llld dd
 |...........|         |.|
 |.A.B.C.D.E.|         |.|
--------.----|         |.|
|.F...G..H.I.|         |.|
|............|         |.|
-----.--------   ------|.|
 |.K..L.M...|  --|.....|.|
 |........N.|  |.+.....|.|
 |.O.....Q.--  |-|.....|.|
-------.----   |.+.....+.|
|.J.P.R..|     |-|.....|--
|........|     |.+.....|
|...------     --|.....|
-----            -------

It is also possible to push D into the 4th room under J and move C to where D is now if you want some more leeway to move boulders around. Now everything is setup to start filling holes. Cleanup most of rooms 2 and 3:

-------------------------- H ruuu luuu r*
|@......^^^^^^^^^^^^^^^^.| G rrrr uuul uuur r*
|.......----------------.| F rrrr rruu uluu urrr*
-------.------         |.| I lllu uulu uurr rr*
 |...........|         |.| C uuuu rrru uulu uurr rrr*
 |.A.B.....E.|         |.| K rruu urrr uuul uuur rrrr r*
--------.----|         |.| L luuu rrru uulu uurr rrrr r*
|.F.G..H...I.|         |.| M lllu uurr ruuu luuu rrrr rrrr*
|............|         |.| N llll luuu urrr uuul uuur rrrr rrrr*
-----.--------   ------|.|
 |.K..L.M...|  --|.....|.|
 |...C....N.|  |.+.....|.|
 |.O..D..Q.--  |-|.....|.|
-------.----   |.+.....+.|
|.J.P.R..|     |-|.....|--
|........|     |.+.....|
|...------     --|.....|
-----            -------

Now there are only a few boulders left with a lot of space. The boulders in room 4 can be cleared directly, the boulders in room 1 and 3 should first be moved through room 3 and 4 respectively:

-------------------------- R ruuu ullu uurr ruuu luuu rrrr rrrr rr*
|@...............^^^^^^^.| P rrru uuul luuu rrru uulu uurr rrrr rrrr r*
|.......----------------.| J rrrr ruuu ullu uurr ruuu luuu rrrr rrrr rrrr*
-------.------         |.| D rddd llll lurr rrru uuul luuu rrru uulu uurr rrrr rrrr rrr*
 |...........|         |.| B rrrd ddll lddd uuuu rrru uulu uurr rrrr rrrr rrrr*
 |.A.B.....E.|         |.| A rrrr rddd llld dduu uurr ruuu luuu rrrr rrrr rrrr rrr*
--------.----|         |.| E llld ddll lddd uuuu rrru uulu uurr rrrr rrrr rrrr rr*     
|............|         |.|
|............|         |.|
-----.--------   ------|.|
 |..........|  --|.....|.|
 |..........|  |.+.....|.|
 |.O..D..Q.--  |-|.....|.|
-------.----   |.+.....+.|
|.J.P.R..|     |-|.....|--
|........|     |.+.....|
|...------     --|.....|
-----            -------

In the large room behind the door is a treasure zoo. Behind one of the three doors in the zoo is a square with the prize and "Elbereth" burnt. In NetHack 3.6.0, there is also a cursed scroll of scare monster. Also remember to check under the boulders O and Q for possible usable items.

--------------------------
|<.......................|
|.......----------------.|
-------.------         |.|
 |...........|         |.|
 |...........|         |.|
--------.----|         |.|
|............|         |.|
|............|         |.|
-----.--------   ------|.|
 |..........|  --|.....|.|
 |..........|  |.+.....|.|
 |.O.....Q.--  |-|.....|.|
-------.----   |.+.....+@|
|........|     |-|.....|--
|........|     |.+.....|
|...------     --|.....|
-----            -------