source: branches/HeuristicLab.Problems.GrammaticalOptimization/HeuristicLab.Problems.GrammaticalOptimization/SantaFeAntProblem.cs @ 11659

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Remoting.Messaging;
using System.Text;

namespace HeuristicLab.Problems.GrammaticalOptimization {
  public class SantaFeAntProblem : IProblem {
    private const string grammarString = @"
G(A):
A -> l | r | m | ?(A)(A) | AA | AAA
";
    // Ant -> left | right | move | if-food-ahead Ant Ant | Ant Ant | Ant Ant Ant


    private readonly IGrammar grammar;

    public SantaFeAntProblem() {
      this.grammar = new Grammar(grammarString);
    }

    public double GetBestKnownQuality(int maxLen) {
      // for now only an upper bound is returned, ideally all food pellets are discovered
      return 89;
    }

    public IGrammar Grammar {
      get { return grammar; }
    }

    public double Evaluate(string sentence) {
      var ant = new Ant();
      int p = 0;
      Run(ant, sentence, ref p);
      return ant.FoodEaten;
    }

    private void Run(Ant ant, string sentence, ref int p) {
      while (!ant.Done()) {
        if (p >= sentence.Length) p = 0; // restart
        switch (sentence[p]) {
          case 'r': {
              ant.TurnRight();
              p++;
              break;
            }
          case 'l': {
              ant.TurnLeft();
              p++;
              break;
            }
          case 'm': {
              ant.Move();
              p++;
              break;
            }
          case '?': {
              p++; // skip p
              if (ant.IsFoodAhead()) {
                if (sentence[p] != '(') throw new ArgumentException();
                p++;
                Run(ant, sentence, ref p);      // it cannot happen that we run over the the end of the sentence here
                if (ant.Done()) return;
                if (sentence[p] != '(') throw new ArgumentException();
                p++;
                Skip(sentence, ref p);
              } else {
                if (sentence[p] != '(') throw new ArgumentException();
                p++;
                Skip(sentence, ref p);
                if (sentence[p] != '(') throw new ArgumentException();
                p++;
                Run(ant, sentence, ref p);    // it cannot happen that we run over the the end of the sentence here
              }
              break;
            }
          case ')': {
              p++; // skip
              return;     // caller must continue processing
            }
          default: {
              throw new ArgumentException();
            }
        }
      }
    }

    private void Skip(string sentence, ref int p) {
      int openCount = 1;
      while (openCount > 0) {
        if (sentence[p] == '(') openCount++;
        else if (sentence[p] == ')') openCount--;
        p++;
      }
    }
  }

  public class Ant {
    private const int maxSteps = 600;
    public enum HeadingEnum { North, East, South, West };
    public int FoodEaten { get; private set; }
    private readonly char[][] world = new char[32][];
    private int posX;
    private int posY;
    private int steps;
    private HeadingEnum heading;

    public Ant() {
      world[00] = " ###                            ".ToCharArray();
      world[01] = "   #                            ".ToCharArray();
      world[02] = "   #                    .###..  ".ToCharArray();
      world[03] = "   #                    #    #  ".ToCharArray();
      world[04] = "   #                    #    #  ".ToCharArray();
      world[05] = "   ####.#####       .##..    .  ".ToCharArray();
      world[06] = "            #       .        #  ".ToCharArray();
      world[07] = "            #       #        .  ".ToCharArray();
      world[08] = "            #       #        .  ".ToCharArray();
      world[09] = "            #       #        #  ".ToCharArray();
      world[10] = "            .       #        .  ".ToCharArray();
      world[11] = "            #       .        .  ".ToCharArray();
      world[12] = "            #       .        #  ".ToCharArray();
      world[13] = "            #       #        .  ".ToCharArray();
      world[14] = "            #       #  ...###.  ".ToCharArray();
      world[15] = "            .   .#...  #        ".ToCharArray();
      world[16] = "            .   .      .        ".ToCharArray();
      world[17] = "            #   .      .        ".ToCharArray();
      world[18] = "            #   #      .#...    ".ToCharArray();
      world[19] = "            #   #          #    ".ToCharArray();
      world[20] = "            #   #          .    ".ToCharArray();
      world[21] = "            #   #          .    ".ToCharArray();
      world[22] = "            #   .      ...#.    ".ToCharArray();
      world[23] = "            #   .      #        ".ToCharArray();
      world[24] = " ..##..#####.   #               ".ToCharArray();
      world[25] = " #              #               ".ToCharArray();
      world[26] = " #              #               ".ToCharArray();
      world[27] = " #     .#######..               ".ToCharArray();
      world[28] = " #     #                        ".ToCharArray();
      world[29] = " .     #                        ".ToCharArray();
      world[30] = " .####..                        ".ToCharArray();
      world[31] = "                                ".ToCharArray();

      posX = 0;
      posY = 0;
      heading = HeadingEnum.East;
      FoodEaten = 0;
      steps = 0;
    }

    public bool Done() {
      return steps > maxSteps;
    }

    public void TurnRight() {
      if (steps <= maxSteps) {
        steps++;
        if (heading == HeadingEnum.West) heading = HeadingEnum.North;
        else heading++;
      }
    }

    public void TurnLeft() {
      if (steps <= maxSteps) {
        steps++;
        if (heading == HeadingEnum.North) heading = HeadingEnum.West;
        else heading--;
      }
    }

    public void Move() {
      if (steps <= maxSteps) {
        steps++;
        MoveInternal(ref posX, ref posY);
        if (world[posY][posX] == '#') {
          FoodEaten++;
          world[posY][posX] = '.';
        }
      }
    }

    private void MoveInternal(ref int posX, ref int posY) {
      switch (heading) {
        case HeadingEnum.North:
          posY = (posY + 31) % 32;
          break;
        case HeadingEnum.East:
          posX = (posX + 1) % 32;
          break;
        case HeadingEnum.South:
          posY = (posY + 1) % 32;
          break;
        case HeadingEnum.West:
          posX = (posX + 31) % 32;
          break;
      }
    }

    public bool IsFoodAhead() {
      int nextPosX = posX;
      int nextPosY = posY;
      MoveInternal(ref nextPosX, ref nextPosY);
      return world[nextPosY][nextPosX] == '#';
    }
  }
}