Sokoban Level 2b

Although this sokoban level has the most boulders it is not very hard. There are 20 boulders and 16 pits. 0 boulder ^ pit @ starting position/downstairs < upstairs

---      --- |....|....---     |.........| |..00|00...@|     |.........| |.....0...---     |.........| |....|....|       |....<....| |-.-      |.........| |..0.|.....|      |.........| |.00.|0.0.0|      |.........| |..0.....0.|      |.........| |.000|0..0.+| |....|..0.0.^^^^^^^^^^^^^^^.| -

Strategy
The following solution solves the level without putting any blocks in an immobile position. Faster solutions which do not leave every boulder free 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 pit (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 pit. ---      --- |....|....---     |.........| |..AB|CD...@|     |.........| |.....E...---    |.........| |....|....|      |....<....| |-.-      |.........| |..F.|.....|      |.........| |.GH.|I.J.K|     |.........| |..L.....M.|     |.........| |.NOP|Q..R.+| |....|..S.T.^^^^^^^^^^^^^^^.| - Make way to the fourth room (lower right) by storing boulders in earlier rooms. It is not necessary to store as many boulders as in this example. Elllrrrrru Guuuuu Nuuuuuur Lrrrrr

---      --- |....|....---     |.........| |.GAB|CDE..>|     |.........| |..N......---    |.........| |....|....|      |....<....| |-.-      |.........| |..F.|.....|      |.........| |..H.|I.J.K|     |.........| |......@LM.|     |.........| |..OP|Q..R.+| |....|..S.T.^^^^^^^^^^^^^^^.| - Clear the 4th room with the exception of I and Q. Rr Trr* Srrrrr* Mddrrrrr* Rdrrrrr* Kdddrrrrrr* Lrrddrrrrrrr* Jdddrrrrrrrrrr*

---      --- |....|....---     |.........| |.GAB|CDE..>|     |.........| |..N......---    |.........| |....|....|      |....<....| |-.-      |.........| |..F.|.....|      |.........| |..H.|I....|     |.........| |..........|     |.........| |..OP|Q....+| |....|.............^^^^^^^^.| - Clear the 3th room (lower left) with the exception of F. Ourrrrrrrddrrrrrrrrr* Purrrrrrrddrrrrrrrrrr* Hldrrrrrrrrddrrrrrrrrrrr*

---      --- |....|....---     |.........| |.GAB|CDE..>|     |.........| |..N......---    |.........| |....|....|      |....<....| |-.-      |.........| |..F.|.....|      |.........| |.@..|I....|     |.........| |..........|     |.........| |....|Q....+| |....|................^^^^^.| - Clear the 2nd room (upper left) with the exception of B. Gddddddrrrrrrrrddrrrrrrrrrrrr* Nldddddrrrrrrrrddrrrrrrrrrrrrr* Addlddddrrrrrrrrddrrrrrrrrrrrrrr* Finish off with the two boulders from the 4th room. Qulllrrrrrrrddrrrrrrrrrrrrrrr* Idlllrrrrrrrddrrrrrrrrrrrrrrrr*

---      --- |....|....---     |.........| |...B|CDE..>|     |.........| |.........---    |.........| |....|....|       |....<....| |-.-      |.........| |..F.|.....|      |.........| |....|.....|     |.........| |..........|      |.........| |....|.....+| |....|.....................@| -