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 PalindromeProblem : ISymbolicExpressionTreeProblem {
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9 | // length of the longest palindrome in the sentence
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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 |
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16 |
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17 | private const string hlGrammarString = @"
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18 | G(S):
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19 | 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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20 | ";
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21 |
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22 | private readonly IGrammar grammar;
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23 | public PalindromeProblem() {
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24 | this.grammar = new Grammar(grammarString);
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25 | this.TreeBasedGPGrammar = new Grammar(hlGrammarString);
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26 | }
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27 |
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28 | public double BestKnownQuality(int maxLen) {
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29 | // the whole sentence is a palindrome
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30 | return maxLen;
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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 | return LongestPalindromicSubstring(sentence).Length;
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39 | }
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40 |
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41 |
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42 | private static string Preprocess(string s) {
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43 | var t = new char[2 * s.Length + 3];
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44 | t[0] = '$';
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45 | t[t.Length - 2] = '#';
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46 | t[t.Length - 1] = '@';
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47 | for (int i = 0; i < s.Length; i++) {
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48 | t[2 * (i) + 1] = '#';
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49 | t[2 * i + 2] = s[i];
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50 | }
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51 |
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52 | return new string(t);
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53 | }
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54 |
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55 | public static string LongestPalindromicSubstring(string str) {
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56 | var tLen = 2 * str.Length + 3;
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57 | var p = new int[tLen];
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58 | var t = Preprocess(str);
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59 |
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60 | var center = 0;
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61 | var right = 0;
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62 | for (int i = 1; i < t.Length - 1; i++) {
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63 | var mirror = 2 * center - i;
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64 | if (right > i) p[i] = Math.Min(right - i, p[mirror]);
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65 | while (t[i + (1 + p[i])] == t[i - (1 + p[i])]) {
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66 | p[i]++;
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67 | }
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68 | if (i + p[i] > right) {
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69 | center = i;
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70 | right = i + p[i];
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71 | }
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72 | }
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73 | var len = 0;
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74 | center = 0;
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75 | for (int i = 0; i < t.Length - 1; i++) {
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76 | if (p[i] > len) {
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77 | center = i;
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78 | len = p[i];
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79 | }
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80 | }
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81 |
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82 | var start = (center - 1 - len) / 2;
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83 | var result = new StringBuilder();
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84 | for (int i = 0; i < len; i++) {
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85 | result.Append(str[start + i]);
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86 | }
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87 | return result.ToString();
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88 | }
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89 |
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90 | public string CanonicalRepresentation(string phrase) {
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91 | return phrase;
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92 | }
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93 |
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94 | public IEnumerable<Feature> GetFeatures(string phrase) {
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95 | throw new NotImplementedException();
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96 | }
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97 |
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98 | public IGrammar TreeBasedGPGrammar { get; private set; }
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99 | public string ConvertTreeToSentence(ISymbolicExpressionTree tree) {
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100 | var sb = new StringBuilder();
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101 | foreach (var s in tree.Root.GetSubtree(0).GetSubtree(0).IterateNodesPrefix()) {
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102 | if (s.Symbol.Name == "S") continue;
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103 | sb.Append(s.Symbol.Name);
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104 | }
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105 | return sb.ToString();
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106 | }
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107 | }
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108 | }
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