Code Golf: Lasers

user_41983 0
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The challenge

The shortest code by character count to input a 2D representation of a board, and output 'true' or 'false' according to the input.

The board is made out of 4 types of tiles:

 # - A solid wall
 x - The target the laser has to hit
 / or \ - Mirrors pointing to a direction (depends on laser direction)
 v, ^, > or < - The laser pointing to a direction (down, up, right and left respectively)

There is only one laser and only one target. Walls must form a solid rectangle of any size, where the laser and target are placed inside. Walls inside the 'room' are possible.

Laser ray shots and travels from its origin to the direction it's pointing. If a laser ray hits the wall, it stops. If a laser ray hits a mirror, it bounces 90 degrees to the direction the mirror points to. Mirrors are two sided, meaning both sides are 'reflective' and may bounce a ray in two ways. If a laser ray hits the laser (^v><) itself, it is treated as a wall (laser beam destroys the beamer and so it'll never hit the target).

Test cases

Input:
    ##########
    #   / \  #
    #        #
    #   \   x#
    # >   /  #
    ########## 
Output:
    true

Input:
    ##########
    #   v x  #
    # /      #
    #       /#
    #   \    #
    ##########
Output:    
    false

Input:
    #############
    #     #     #
    # >   #     #
    #     #     #
    #     #   x #
    #     #     #
    #############
Output:
    false

Input:
    ##########
    #/\/\/\  #
    #\\//\\\ #
    #//\/\/\\#
    #\/\/\/x^#
    ##########
Output:
    true

Code count includes input/output (i.e full program).

rosetta-stone code-golf language-agnostic
28 Answers

F# - 454 (or thereabouts)

Bit late to the game, but can't resist posting my 2d attempt.

Update modified slightly. Now stops correctly if transmitter is hit. Pinched Brian's idea for IndexOfAny (shame that line is so verbose). I haven't actually managed to work out how to get ReadToEnd to return from the Console, so I'm taking that bit on trust...

I'm pleased with this answer, as though it is quite short, it is still fairly readable.

let s=System.Console.In.ReadToEnd()       //(Not sure how to get this to work!)
let w=s.IndexOf('\n')+1                   //width
let h=(s.Length+1)/w                      //height
//wodge into a 2d array
let a=Microsoft.FSharp.Collections.Array2D.init h (w-1)(fun y x -> s.[y*w+x])
let p=s.IndexOfAny[|'^';'<';'>';'v'|]     //get start pos
let (dx,dy)=                              //get initial direction
 match "^<>v".IndexOf(s.[p]) with
 |0->(0,-1)
 |1->(-1,0)
 |2->(1,0)
 |_->(0,1)
let mutable(x,y)=(p%w,p/w)                //translate into x,y coords
let rec f(dx,dy)=
 x<-x+dx;y<-y+dy                          //mutate coords on each call
 match a.[y,x] with
 |' '->f(dx,dy)                           //keep going same direction
 |'/'->f(-dy,-dx)                         //switch dx/dy and change sign
 |'\\'->f(dy,dx)                          //switch dx/dy and keep sign
 |'x'->"true"
 |_->"false"
System.Console.Write(f(dx,dy))
Benjol_114100
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