How to program

This guide covers input and output type format, as well as available commands. If you wish to solve a problem instance named Inputs/<problem-instance>.in, you are expected to put your solution in a file named Outputs/<problem-instance>.out.

Internal coordinate representation

when seeing certain messages, you will encounter the coordinates in this format unless stated otherwise (e.g. the game reports an error specifying a graph edge)
the game uses the (y,x) (also referred to as (row,col)) coordinate system with its origin being at the top-left corner of the grid
- the x-coordinate increases by going right (east), the y-coordinate increases by going down (south)
- beware, the top-left corner is actually at (1,1) (that's because lua arrays are designed as 1-indexed 😎) Example (padded with extra spaces for clarity)

row/col 1  2  3 4 5 6   7   8
   1    #  #  # # # #   #   #
   2    #  .  . # . .   E   #
   3    #  .  . I . .   #   #
   4    #  #  . . . .   .   #
   5    #  .  . I # I (5,7) #
   6    #  .  . . . #   .   #
   7    #  IS # I . I   #   #
   8    #  #  # # # #   #   #

Orientation

there are 4 directions, one of which the robot will be facing: North, East, South, West
moving North decreases the y (row) coordinate of the robot
moving East increases the x (col) coordinate of the robot
moving South increases the y (row) coordinate of the robot
moving West decreases the x (col) coordinate of the robot
Eralk's default orientation is to North

Robot commands

in the following examples, Eralk is marked as one of nesw denoting his orientation in the maze
start and end cells are omitted for better alignment and readability
TURN_LEFT
- formally, this command changes the robot's orientation like this (the format is Old orientation -> New orientation): North -> West, West -> South, South -> East, East -> North

# # # #                # # # #                # # # #                # # # #                # # # #
# n . #                # w . #                # s . #                # e . #                # n . #
# . . # -> TURNLEFT -> # . . # -> TURNLEFT -> # . . # -> TURNLEFT -> # . . # -> TURNLEFT -> # . . #
# . . #                # . . #                # . . #                # . . #                # . . #
# # # #                # # # #                # # # #                # # # #                # # # #

TURN_RIGHT
- inverse operation to the TURN_LEFT command
COLLECT
- this command makes Eralk collect ONE item at the current position and adds it to Eralk's inventory
- if there's no item to be collected, this command functions as a NOP except that you get a warning in stderr (which you can safely ignore if you don't care)
DROP
- Eralk drops ONE item at the current position from his inventory
- if Eralk's inventory is empty, this command functions as a NOP except that you get a warning in stderr (which you can safely ignore if you don't care)
MOVE_TO_ITEM
if there's a wall somewhere between Eralk and the closest item in his direction, this command functions as MOVE_TO_WALL
otherwise Eralk makes at least one step in the direction of his current orientation and stops at the closest item detected underneath him

# #  # # # # #                  # # #  # # # #
# .  I . . . #                  # . I  . . . #
# # Ie I I # # -> MOVETOITEM -> # # I Ie I # #
# .  . . . . #                  # . .  . . . #
# #  # # # # #                  # # #  # # # #

# # # # #                  # # # # #
# . # . #                  # . # . #
# . . . #                  # . n . #
# . . . # -> MOVETOITEM -> # . . . # (acts as MOVETOWALL)
# . . . #                  # . . . #
# . n . #                  # . . . #
# # # # #                  # # # # #

# # # # #                  # # # # #
# . I . #                  # . I . #
# . I . #                  # . I . #
# . # . # -> MOVETOITEM -> # . # . # (acts as MOVETOWALL)
# . . . #                  # . n . #
# . n . #                  # . . . #
# # # # #                  # # # # #

MOVE_TO_WALL
- move in the current direction until there's a wall one step away from Eralk
- in this command Eralk makes ZERO or more steps (that is, he may not need to move at all if standing in front of a wall already)
MOVE_TO_START
- makes Eralk move in the current direction until he's standing at a cell marked as start S
- if there's no start in the current direction, this command functions as MOVE_TO_WALL
- in this command Eralk makes ZERO or more steps (that is, he may not need to move at all if standing on start already)
MOVE_TO_END
- makes Eralk move in the current direction until he's standing at a cell marked as end E
- if there's no start in the current direction, this command functions as MOVE_TO_WALL
- in this command Eralk makes ZERO or more steps (that is, he may not need to move at all if standing on end already)
NOP
- it does absolutely nothing lol

Input file (problem instance) description

the first line in the file contains a lowercase single-word string determining the game type (=problem class)
on the next line follow two space-separated positive integers h w denoting the height and the width of the grid, respectively, measured in cells
next follow h lines, each containing precisely w space-separated cell type descriptions

sortp
10 10
# # # # # # # # # #
# . . . . # . . E #
# . . . . I . . # #
# . . # . . . . . #
# . . I . I # . . #
# # . . . . . # . #
# . . I # I . I # #
# . . . . # . . . #
# IS # I . I # I . #
# # # # # # # # # #

Cell types

a cell can be one or more of:
- empty (denoted by the char .)
- non-empty:
  - item (denoted by the char I)
    - items don't have any internal identifiers, they are indistinguishable from one another
  - start (S)
  - end (E)
  - wall (#)
cell types may be combined (e.g. you may encounter SEI meaning there's start, end and a single item on this cell), however you will never encounter a cell that is described nboth as empty and non-empty at the same time (e.g. .I is a forbidden cell description)
there may be multiple items at a single cell (e.g. EIIIIS), but there will never be more than one start, end, wall or empty
there is always precisely one start and one end
each cell either is a wall or has wall neighbours in all 4 directions
cell type order is arbitrary

Output file format

sequence of commands that the robot shall execute in the order given in this file
there is no size limit (yet)
the parser is pretty chill about the user input
commands are read in a case-insensitive way, you can even put dashes or underscores inside them if you feel like it
- e.g. all MOVETOWALL, movetowall, move-to-wall or moveToWall are recognized as the same command
other non-letter characters (that is, besides - and _) are treated as command separators

Eralk documentation