1 | using System;
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2 | using System.Collections.Generic;
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3 | using System.Linq;
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4 | using System.Text;
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5 | using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
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6 |
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7 | namespace HeuristicLab.Problems.GrammaticalOptimization {
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8 | public class HardPalindromeProblem : ISymbolicExpressionTreeProblem {
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9 | // length of the longest palindrome in the sentence + number of different symbols occurring in the palindrome
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10 | private const string grammarString = @"
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11 | G(S):
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12 | S -> T | TS
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13 | T -> a .. z
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14 | ";
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15 | private const string hlGrammarString = @"
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16 | G(S):
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17 | S -> a | b | c | d | e | f | g | h | i | j | k | l | m | n | o | p | q | r | s | t | u | v | w | x | y | z | SS
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18 | ";
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19 |
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20 | private readonly IGrammar grammar;
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21 | public HardPalindromeProblem() {
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22 | this.grammar = new Grammar(grammarString);
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23 | this.TreeBasedGPGrammar = new Grammar(hlGrammarString);
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24 | }
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25 |
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26 | public double BestKnownQuality(int maxLen) {
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27 | // the whole sentence is a palindrome + each symbol occurs only once or twice
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28 | // for odd total length the number of different characters can be larger than len/2 (aba)
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29 | // the second part is limited to 26 different characters
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30 | return maxLen + Math.Min(26, (maxLen + 1) / 2);
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31 | }
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32 |
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33 | public IGrammar Grammar {
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34 | get { return grammar; }
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35 | }
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36 |
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37 | public double Evaluate(string sentence) {
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38 | var palindrome = PalindromeProblem.LongestPalindromicSubstring(sentence);
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39 | var palindromeBytes = ASCIIEncoding.ASCII.GetBytes(palindrome);
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40 | var chrCount = new int[256];
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41 | foreach (var b in palindromeBytes) {
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42 | chrCount[b]++;
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43 | }
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44 | return palindrome.Length + chrCount.Count(c => c > 0);
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45 | }
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46 |
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47 | public string CanonicalRepresentation(string phrase) {
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48 | return phrase;
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49 | }
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50 |
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51 | public IEnumerable<Feature> GetFeatures(string phrase)
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52 | {
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53 | throw new NotImplementedException();
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54 | }
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55 |
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56 | public IGrammar TreeBasedGPGrammar { get; private set; }
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57 | public string ConvertTreeToSentence(ISymbolicExpressionTree tree) {
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58 | var sb = new StringBuilder();
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59 | foreach (var s in tree.Root.GetSubtree(0).GetSubtree(0).IterateNodesPrefix()) {
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60 | if (s.Symbol.Name == "S") continue;
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61 | sb.Append(s.Symbol.Name);
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62 | }
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63 | return sb.ToString();
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64 | }
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65 | }
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66 | }
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