docs: add spaceship

notes/sor4chi.md

@@ -34,3 +34,9 @@ ou scored some points for using the echo service!
 `get lambdaman`を送信。
 
 [これが帰ってきた](./lambdaman/intro.md)
+
+### [2:42] `get speaceship`する
+
+`get spaceship`を送信。
+
+[これが帰ってきた](./spaceship/intro.md)

notes/spaceship/intro.md

@@ -0,0 +1,43 @@
+Welcome to the Spaceship course!
+
+In 2020, most of us have learned how to operate a spaceship. In this course we'll play a small chess-like game featuring the spaceship! The game operates on an infinite 2D chess board, with the spaceship initially located on `(0,0)`. The spaceship has a velocity `vx` and `vy`, which are initially both set to `0`. In each turn the player can increase/decrease each of those numbers by at most one, and then the piece moves `vx` steps to the right and `vy` steps up.
+
+Moves are represented with a single digit, inspired by the old numeric pad on a computer keyboard that we used to have in the old days on Earth. For example, `7` means decreasing `vx` and increasing `vy` by `1`, while `6` means increasing `vx` by `1` and keeping `vy` the same. A path can then be represented by a sequence of digits, e.g. the path `236659` visits, in this order, the following squares: `(0,0) (0,-1) (1,-3) (3,-5) (6,-7) (9,-9) (13,-10)`.
+
+Now the challenge is the following: given a list of squares to be visited, find a sequence of moves that visits all those squares. our solution may consist of at most `10,000,000` moves.
+
+The following levels are available:
+* [spaceship1] Best score: 5.
+* [spaceship2] Best score: 49.
+* [spaceship3] Best score: 10.
+* [spaceship4] Best score: 99.
+* [spaceship5] Best score: 119.
+* [spaceship6] Best score: 123.
+* [spaceship7] Best score: 94.
+* [spaceship8] Best score: 104.
+* [spaceship9] Best score: 260.
+* [spaceship10] Best score: 405.
+* [spaceship11] Best score: 8192.
+* [spaceship12] Best score: 8192.
+* [spaceship13] Best score: 31744.
+* [spaceship14] Best score: 210.
+* [spaceship15] Best score: 43.
+* [spaceship16] Best score: 1975.
+* [spaceship17] Best score: 440.
+* [spaceship18] Best score: 1959.
+* [spaceship19] Best score: 15323.
+* [spaceship20] Best score: 4186.
+* [spaceship21] Best score: 4243.
+* [spaceship22] Best score: 1359.
+* [spaceship23] Best score: 385814.
+* [spaceship24] Best score: 799788.
+* [spaceship25] Best score: 894411.
+
+To submit a solution, send an ICFP expression that evaluates to:
+
+```
+solve spaceshipX moves
+```
+
+our score is the number of moves, so a lower score is better.
+