Ice Golf Challenge

Question

The goal of this challenge is to write a program or function that returns the least amount of strikes needed to complete a given course.

Input

• The layout of the course can be passed in any suitable way and format you prefer. (read from the console, passed as an input parameter, read from a file or any other, multiline-string, string array, two-dimensional character/byte array).
• The start position of the ball and the hole can be passed as input too, it doesn't have to be parsed from the input. In the test-cases they are included in the course to make sure there is no confusion about the actual position.
• You can remap the input characters to something else, as long as they are still recognisable as distinct characters (e.g. printable ASCII characters).

Output

• The program must return the lowest possible score (least amount of strikes needed to reach the hole) for any course passed as input in a sensible format (string, integer, float or a haiku describing the result)
• If the course is impossible to beat, return -1 (or any other falsy value of your choice that wouldn't be returned for a beatable course).

Example:

In this example positions are notated 0-based, X/Y, left-to-right, top-down - but you can use any format you like since the result is completely format-independent anyways.

Input:

###########
#     ....# 
#      ...# 
#  ~    . # 
# ~~~   . # 
# ~~~~    # 
# ~~~~    # 
# ~~~~  o # 
# ~~~~    # 
#@~~~~    # 
###########

Ball (Start-Position): 1/9
Hole (End-Position):   8/7

Output:

8

Rules and fields

The course can consist of the following fields:

• '@' Ball - The start of the course
• 'o' Hole - The goal of the course
• '#' Wall - Ball will stop when it hits a wall
• '~' Water - Must be avoided
• '.' Sand - Ball will stop on sand immediately
• ' ' Ice - Ball will continue to slide until it hits something

The basic rules and restrictions of the game:

• The ball can't move diagonally, only left, right, up and down.
• The ball will not stop in front of water, only in front of walls, on sand and in the hole.
  • Shots into the water are invalid/impossible
  • The ball will stay in the hole, not skip over it like it would on ice
• The course is always rectangular.
• The course is always bordered by water or walls (no boundary checks required).
• There is always exactly one ball and one hole.
• Not all courses are possible to beat.
• There might be multiple paths that result in the same (lowest) score.

Loopholes and Winning Condition

• Standard loopholes are forbidden
• Programs must terminate
• You can't make up additional rules (hitting the ball so hard it skips over water, rebounds off a wall, jumps over sand fields, curves around corners, etc.)
• This is code-golf, so the solution with the least amount of characters wins.
• Solutions must be able to handle all provided test-cases, if this is impossible due to restrictions of the used language please specify that in your answer.

Test cases

Course #1 (2 strikes)

####
# @#
#o~#
####

Course #2 (not possible)

#####
#@  #
# o #
#   #
#####

Course #3 (3 strikes)

~~~
~@~
~.~
~ ~
~ ~
~ ~
~ ~
~.~
~o~
~~~

Course #4 (2 strikes)

#########
#~~~~~~~#
#~~~@~~~#
##  .  ##
#~ ~ ~ ~#
#~. o .~#
#~~~ ~~~#
#~~~~~~~#
#########

Course #5 (not possible)

~~~~~~~
~...  ~
~.@.~.~
~...  ~
~ ~ ~.~
~ . .o~
~~~~~~~

More Test cases:

https://pastebin.com/Azdyym00

Answer 1

JavaScript (ES6), 174 bytes

Takes input in curling currying syntax ([x, y])(a), where x and y are the 0-indexed coordinates of the starting position and a[ ] is a matrix of integers, with 0 = ice, 1 = wall, 2 = sand, 3 = hole and 4 = water

Returns 0 if there's no solution.

p=>a=>(r=F=([x,y],n,R=a[y],c=R[x])=>R[c&(R[x]=4)|n>=r||[-1,0,1,2].map(d=>(g=_=>(k=a[v=Y,Y+=d%2][h=X,X+=~-d%2])||g())(X=x,Y=y)>3?0:k>2?r=-~n:F(k>1?[X,Y]:[h,v],-~n)),x]=c)(p)|r

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Commented

p => a => (                       // given the starting position p[] and the matrix a[]
  r =                             // r = best result, initialized to a non-numeric value
  F = (                           // F = recursive function taking:
    [x, y],                       //   (x, y) = current position
    n,                            //   n = number of shots, initially undefined
    R = a[y],                     //   R = current row in the matrix
    c = R[x]                      //   c = value of the current cell
  ) =>                            //
    R[                            // this will update R[x] once the inner code is executed
      c & (R[x] = 4) |            //   set the current cell to 4 (water); abort if it was
      n >= r ||                   //   already set to 4 or n is greater than or equal to r
      [-1, 0, 1, 2].map(d =>      //   otherwise, for each direction d:
        (g = _ => (               //     g = recursive function performing the shot by
          k = a[                  //         saving a backup (h, v) of (X, Y)
            v = Y, Y += d % 2][   //         and updating (X, Y) until we reach a cell
            h = X, X += ~-d % 2]) //         whose value k is not 0 (ice)
          || g()                  //   
        )(X = x, Y = y)           //     initial call to g() with (X, Y) = (x, y)
        > 3 ?                     //     if k = 4 (water -> fail):
          0                       //       abort immediately
        :                         //     else:
          k > 2 ?                 //       if k = 3 (hole -> success):
            r = -~n               //         set r to n + 1
          :                       //       else:
            F(                    //         do a recursive call to F():
              k > 1 ?             //           if k = 2 (sand):
                [X, Y]            //             start the next shots from the last cell
              :                   //           else (wall):
                [h, v],           //             start from the last ice cell
              -~n                 //           increment the number of shots
            )                     //         end of recursive call
      ), x                        //   end of map(); x = actual index used to access R[]
    ] = c                         // restore the value of the current cell to c
)(p) | r                          // initial call to F() at the starting position; return r

Answer 2

Python 3, 273 bytes

def p(g,c,d,k=0):
	while 1>k:c+=d;k=g.get(c,9)
	return-(k==2)or c-d*(k==3)
def f(g):
	c={q for q in g if g.get(q,9)>4};I=0;s=[c]
	while all(g.get(q,9)-4for q in c):
		c={k for k in{p(g,k,1j**q)for k in c for q in range(4)}if-~k}
		if c in s:return-1
		s+=[c];I+=1
	return I

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-41 bytes thanks to ovs
-1 byte thanks to Jonathan Frech

Answer 3

C#, 461 418 bytes

This is just a non-competitive reference implementation to (hopefully) revive this challenge:

Golfed by Kevin Cruijssen

int P(string[]C){int w=C[0].Length,i=0,l=c.Length;var c=string.Join("",C);var h=new int[l];for(var n=new List<int>();i<l;n.Add(i++))h[i]=c[i]!='@'?int.MaxValue:0;for(i=1;;i++){var t=n;n=new List<int>();foreach(int x in t){foreach(int d in new[]{-1,1,-w,w}){for(int j=x+d;c[j]==' ';j+=d);if(c[j]=='#'&h[j-d]>s){h[j-d]=s;n.Add(j-d);}if(c[j]=='.'&h[j]>s){h[j]=s;n.Add(j);}if(c[j]=='o')return s;}}if(n.Count<1)return -1;}}

Ungolfed

int IceGolf(string[] course)
{
    // Width of the course
    int w = course[0].Length;
    
    // Course as single string
    var c = string.Join("", course);
    
    // Array of hits per field
    var hits = new int[c.Length];
    
    // Fields to continue from
    var nextRound = new List<int>();

    // Initialize hits
    for (int i = 0; i < hits.Length; i++)
    {
        if (c[i] != '@')
            // All fields start with a high value
            hits[i] = Int32.MaxValue;
        else
        {
            // Puck field starts with 0
            hits[i] = 0;
            nextRound.Add(i);
        }
    }

    for (int s = 1; ; s++)
    {
        // clear the fields that will be used in the next iteration
        var thisRound = nextRound;
        nextRound = new List<int>();

        foreach (int i in thisRound)
        {
            // test all 4 directions
            foreach (int d in new[] { -1, 1, -w, w })
            {
                int j = i+d;
                
                // ICE - slide along
                while (c[j] == ' ')
                    j += d;

                // WALL - stop on previous field
                if (c[j] == '#' && hits[j-d] > s)
                {
                    hits[j-d] = s;
                    nextRound.Add(j-d);
                }
                
                // SAND - stop
                if (c[j] == '.' && hits[j] > s)
                {
                    hits[j] = s;
                    nextRound.Add(j);
                }
                
                // HOLE return strikes
                if (c[j] == 'o')
                    return s;
            }
        }
        
        // No possible path found
        if (nextRound.Count == 0)
            return -1;
    }
}

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