# Sokoban Level 3i

Sokoban Level 3i is one of the new maps for Sokoban in some variants of NetHack. It appears as a possible second floor map for Sokoban in UnNetHack, and may appear as a third level map in GruntHack and EvilHack. It has 17 boulders and 14 holes, leaving 3 spare boulders.

In UnNetHack, like all Sokoban levels it may be flipped horizontally or vertically.

```---------                 0 boulder
|.......|                 ^ hole
--...0.--                 > starting position/downstairs
--.0.------------------- < upstairs
|-.--..^^^^^^^^^^^^^^.| + door
|.>....--------------+|
|0.--..|----    |.....|
|.00..--...|    |.....|
--0..---.0..|    |.....|
|.0..|....0--    |..<..|
|...0|.0...|     |.....|
--0...0.00.|     |.....|
|.0.|.0.---     |.....|
--..|...|       -------
|..|----
----
```

## Strategy

The following solution may not be very fast or organized. Improvements welcome. Like all Sokoban levels it can be solved without making any boulders 'stick'.

All boulders are replaced by letters so they can be referred to. Letters O and Q are skipped for clarity. 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 "N ddrr*" means move boulder N two times down and two times to the right into a hole.

The first thing to do is move the boulders so that boulder C can be moved downward:

```---------                 D d
|.......|                 E r
--...A.--                 M r
--.B.------------------- N uu
|-.--..^^^^^^^^^^^^^^.| M r
|.@....--------------+| J drrr
|C.--..|----    |.....| R d
|.DE..--...|    |.....| D ddd
--F..---.G..|    |.....| H r
|.H..|....I--    |..<..| F d
|...J|.K...|     |.....| C d
--L...M.NP.|     |.....|
|.R.|.S.---     |.....|
--..|...|       -------
|..|----
----
```

The boulders in the left half of the level can now be solved:

```---------                 E lluu ____ _ rrrr ur*
|.......|                 H uuuu ____ _ rrrr urr*
--...A.--                 F ruuu u___ _ rrrr urrr*
--.B.------------------- C druu uu__ _ rrrr urrr r*
|-.--..^^^^^^^^^^^^^^.| B uddd du__ _ rrrr urrr rr*
|.>....--------------+| A lddd du__ _ rrrr urrr rrr*
|@.--..|----    |.....| D uuuu uu__ _ rrrr urrr rrrr*
|C..E.--...|    |.....| R uuuu uuuu _ rrrr urrr rrrr r*
--...---.G..|    |.....| L uuru uuu_ _ rrrr urrr rrrr rr*
|.FH.|..N.I--    |..<..|
|....|.K...|     |.....|
--LD...JMP.|     |.....|
|...|.S.---     |.....|
--R.|...|       -------
|..|----
----
```

The sideways "T" boulder formation provides the final boulders needed fill the remaining holes:

```---------                 M u
|.......|                 J llll ___ uuuu uurr rrur rrrr rrrr r*
--.....--                 S ulll l__ uuuu uurr rrur rrrr rrrr rr*
--...------------------- K dlll l__ uuuu uurr rrur rrrr rrrr rrr*
|-.--.........@.^^^^^.| N r
|.>....--------------+| M dd
|..--..|----    |.....| P llll ll_ uuuu uurr rrur rrrr rrrr rrrr*
|.....--...|    |.....| M ulll ll_ uuuu uurr rrur rrrr rrrr rrrr r*
--...---.G..|    |.....|
|....|..N.I--    |..<..|
|....|.K...|     |.....|
--.....JMP.|     |.....|
|...|.S.---     |.....|
--..|...|       -------
|..|----
----
```

The level is now complete. You may want to check under and behind the last few boulders for items:

```---------
|.......|
--.....--
--...-------------------
|-.--..............@..|
|.>....--------------+|
|..--..|----    |.....|
|.....--...|    |.....|
--...---.G..|    |.....|
|....|...NI--    |..<..|
|....|.....|     |.....|
--.........|     |.....|
|...|...---     |.....|
--..|...|       -------
|..|----
----
```