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| <a href="_levenshtein_distance_8cs.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="comment">/*</span></div> |
| <div class="line"><a name="l00002"></a><span class="lineno"> 2</span> <span class="comment"> * Licensed to the Apache Software Foundation (ASF) under one or more</span></div> |
| <div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="comment"> * contributor license agreements. See the NOTICE file distributed with</span></div> |
| <div class="line"><a name="l00004"></a><span class="lineno"> 4</span> <span class="comment"> * this work for additional information regarding copyright ownership.</span></div> |
| <div class="line"><a name="l00005"></a><span class="lineno"> 5</span> <span class="comment"> * The ASF licenses this file to You under the Apache License, Version 2.0</span></div> |
| <div class="line"><a name="l00006"></a><span class="lineno"> 6</span> <span class="comment"> * (the "License"); you may not use this file except in compliance with</span></div> |
| <div class="line"><a name="l00007"></a><span class="lineno"> 7</span> <span class="comment"> * the License. You may obtain a copy of the License at</span></div> |
| <div class="line"><a name="l00008"></a><span class="lineno"> 8</span> <span class="comment"> *</span></div> |
| <div class="line"><a name="l00009"></a><span class="lineno"> 9</span> <span class="comment"> * http://www.apache.org/licenses/LICENSE-2.0</span></div> |
| <div class="line"><a name="l00010"></a><span class="lineno"> 10</span> <span class="comment"> *</span></div> |
| <div class="line"><a name="l00011"></a><span class="lineno"> 11</span> <span class="comment"> * Unless required by applicable law or agreed to in writing, software</span></div> |
| <div class="line"><a name="l00012"></a><span class="lineno"> 12</span> <span class="comment"> * distributed under the License is distributed on an "AS IS" BASIS,</span></div> |
| <div class="line"><a name="l00013"></a><span class="lineno"> 13</span> <span class="comment"> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</span></div> |
| <div class="line"><a name="l00014"></a><span class="lineno"> 14</span> <span class="comment"> * See the License for the specific language governing permissions and</span></div> |
| <div class="line"><a name="l00015"></a><span class="lineno"> 15</span> <span class="comment"> * limitations under the License.</span></div> |
| <div class="line"><a name="l00016"></a><span class="lineno"> 16</span> <span class="comment"> */</span></div> |
| <div class="line"><a name="l00017"></a><span class="lineno"> 17</span> </div> |
| <div class="line"><a name="l00018"></a><span class="lineno"> 18</span> <span class="keyword">using</span> System;</div> |
| <div class="line"><a name="l00019"></a><span class="lineno"> 19</span> <span class="keyword">using</span> System.Collections.Generic;</div> |
| <div class="line"><a name="l00020"></a><span class="lineno"> 20</span> <span class="keyword">using</span> System.Text;</div> |
| <div class="line"><a name="l00021"></a><span class="lineno"> 21</span> <span class="keyword">using</span> <a class="code" href="class_spell_checker_1_1_net_1_1_search_1_1_spell_1_1_spell_checker.html">SpellChecker</a>.Net.Search.Spell;</div> |
| <div class="line"><a name="l00022"></a><span class="lineno"> 22</span> </div> |
| <div class="line"><a name="l00023"></a><span class="lineno"> 23</span> <span class="keyword">namespace </span><a class="code" href="class_spell_checker_1_1_net_1_1_search_1_1_spell_1_1_spell_checker.html">SpellChecker</a>.Net.Search.Spell</div> |
| <div class="line"><a name="l00024"></a><span class="lineno"> 24</span> {</div> |
| <div class="line"><a name="l00028"></a><span class="lineno"><a class="code" href="class_spell_checker_1_1_net_1_1_search_1_1_spell_1_1_levenshtein_distance.html"> 28</a></span>  <span class="keyword">public</span> <span class="keyword">class </span><a class="code" href="class_spell_checker_1_1_net_1_1_search_1_1_spell_1_1_levenshtein_distance.html" title="Levenshtein edit distance ">LevenshteinDistance</a> : <a class="code" href="interface_spell_checker_1_1_net_1_1_search_1_1_spell_1_1_string_distance.html" title="Interface for string distances. ">StringDistance</a></div> |
| <div class="line"><a name="l00029"></a><span class="lineno"> 29</span>  {</div> |
| <div class="line"><a name="l00038"></a><span class="lineno"><a class="code" href="class_spell_checker_1_1_net_1_1_search_1_1_spell_1_1_levenshtein_distance.html#a4131ec2751ef745b425446af7a44bc0d"> 38</a></span>  <span class="keyword">public</span> <span class="keywordtype">float</span> GetDistance(String target, String other)</div> |
| <div class="line"><a name="l00039"></a><span class="lineno"> 39</span>  {</div> |
| <div class="line"><a name="l00040"></a><span class="lineno"> 40</span>  <span class="keywordtype">char</span>[] sa;</div> |
| <div class="line"><a name="l00041"></a><span class="lineno"> 41</span>  <span class="keywordtype">int</span> n;</div> |
| <div class="line"><a name="l00042"></a><span class="lineno"> 42</span>  <span class="keywordtype">int</span>[] p; <span class="comment">//'previous' cost array, horizontally</span></div> |
| <div class="line"><a name="l00043"></a><span class="lineno"> 43</span>  <span class="keywordtype">int</span>[] d; <span class="comment">// cost array, horizontally</span></div> |
| <div class="line"><a name="l00044"></a><span class="lineno"> 44</span>  <span class="keywordtype">int</span>[] _d; <span class="comment">//placeholder to assist in swapping p and d</span></div> |
| <div class="line"><a name="l00045"></a><span class="lineno"> 45</span> </div> |
| <div class="line"><a name="l00046"></a><span class="lineno"> 46</span>  <span class="comment">/*</span></div> |
| <div class="line"><a name="l00047"></a><span class="lineno"> 47</span> <span class="comment"> The difference between this impl. and the previous is that, rather</span></div> |
| <div class="line"><a name="l00048"></a><span class="lineno"> 48</span> <span class="comment"> than creating and retaining a matrix of size s.length()+1 by t.length()+1,</span></div> |
| <div class="line"><a name="l00049"></a><span class="lineno"> 49</span> <span class="comment"> we maintain two single-dimensional arrays of length s.length()+1. The first, d,</span></div> |
| <div class="line"><a name="l00050"></a><span class="lineno"> 50</span> <span class="comment"> is the 'current working' distance array that maintains the newest distance cost</span></div> |
| <div class="line"><a name="l00051"></a><span class="lineno"> 51</span> <span class="comment"> counts as we iterate through the characters of String s. Each time we increment</span></div> |
| <div class="line"><a name="l00052"></a><span class="lineno"> 52</span> <span class="comment"> the index of String t we are comparing, d is copied to p, the second int[]. Doing so</span></div> |
| <div class="line"><a name="l00053"></a><span class="lineno"> 53</span> <span class="comment"> allows us to retain the previous cost counts as required by the algorithm (taking</span></div> |
| <div class="line"><a name="l00054"></a><span class="lineno"> 54</span> <span class="comment"> the minimum of the cost count to the left, up one, and diagonally up and to the left</span></div> |
| <div class="line"><a name="l00055"></a><span class="lineno"> 55</span> <span class="comment"> of the current cost count being calculated). (Note that the arrays aren't really</span></div> |
| <div class="line"><a name="l00056"></a><span class="lineno"> 56</span> <span class="comment"> copied anymore, just switched...this is clearly much better than cloning an array</span></div> |
| <div class="line"><a name="l00057"></a><span class="lineno"> 57</span> <span class="comment"> or doing a System.arraycopy() each time through the outer loop.)</span></div> |
| <div class="line"><a name="l00058"></a><span class="lineno"> 58</span> <span class="comment"></span></div> |
| <div class="line"><a name="l00059"></a><span class="lineno"> 59</span> <span class="comment"> Effectively, the difference between the two implementations is this one does not</span></div> |
| <div class="line"><a name="l00060"></a><span class="lineno"> 60</span> <span class="comment"> cause an out of memory condition when calculating the LD over two very large strings.</span></div> |
| <div class="line"><a name="l00061"></a><span class="lineno"> 61</span> <span class="comment"> */</span></div> |
| <div class="line"><a name="l00062"></a><span class="lineno"> 62</span> </div> |
| <div class="line"><a name="l00063"></a><span class="lineno"> 63</span>  sa = target.ToCharArray();</div> |
| <div class="line"><a name="l00064"></a><span class="lineno"> 64</span>  n = sa.Length;</div> |
| <div class="line"><a name="l00065"></a><span class="lineno"> 65</span>  p = <span class="keyword">new</span> <span class="keywordtype">int</span>[n + 1];</div> |
| <div class="line"><a name="l00066"></a><span class="lineno"> 66</span>  d = <span class="keyword">new</span> <span class="keywordtype">int</span>[n + 1];</div> |
| <div class="line"><a name="l00067"></a><span class="lineno"> 67</span>  <span class="keywordtype">int</span> m = other.Length;</div> |
| <div class="line"><a name="l00068"></a><span class="lineno"> 68</span> </div> |
| <div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  <span class="keywordflow">if</span> (n == 0 || m == 0)</div> |
| <div class="line"><a name="l00070"></a><span class="lineno"> 70</span>  {</div> |
| <div class="line"><a name="l00071"></a><span class="lineno"> 71</span>  <span class="keywordflow">if</span> (n == m)</div> |
| <div class="line"><a name="l00072"></a><span class="lineno"> 72</span>  {</div> |
| <div class="line"><a name="l00073"></a><span class="lineno"> 73</span>  <span class="keywordflow">return</span> 1;</div> |
| <div class="line"><a name="l00074"></a><span class="lineno"> 74</span>  }</div> |
| <div class="line"><a name="l00075"></a><span class="lineno"> 75</span>  <span class="keywordflow">else</span></div> |
| <div class="line"><a name="l00076"></a><span class="lineno"> 76</span>  {</div> |
| <div class="line"><a name="l00077"></a><span class="lineno"> 77</span>  <span class="keywordflow">return</span> 0;</div> |
| <div class="line"><a name="l00078"></a><span class="lineno"> 78</span>  }</div> |
| <div class="line"><a name="l00079"></a><span class="lineno"> 79</span>  }</div> |
| <div class="line"><a name="l00080"></a><span class="lineno"> 80</span> </div> |
| <div class="line"><a name="l00081"></a><span class="lineno"> 81</span> </div> |
| <div class="line"><a name="l00082"></a><span class="lineno"> 82</span>  <span class="comment">// indexes into strings s and t</span></div> |
| <div class="line"><a name="l00083"></a><span class="lineno"> 83</span>  <span class="keywordtype">int</span> i; <span class="comment">// iterates through s</span></div> |
| <div class="line"><a name="l00084"></a><span class="lineno"> 84</span>  <span class="keywordtype">int</span> j; <span class="comment">// iterates through t</span></div> |
| <div class="line"><a name="l00085"></a><span class="lineno"> 85</span> </div> |
| <div class="line"><a name="l00086"></a><span class="lineno"> 86</span>  <span class="keywordtype">char</span> t_j; <span class="comment">// jth character of t</span></div> |
| <div class="line"><a name="l00087"></a><span class="lineno"> 87</span> </div> |
| <div class="line"><a name="l00088"></a><span class="lineno"> 88</span>  <span class="keywordtype">int</span> cost; <span class="comment">// cost</span></div> |
| <div class="line"><a name="l00089"></a><span class="lineno"> 89</span> </div> |
| <div class="line"><a name="l00090"></a><span class="lineno"> 90</span>  <span class="keywordflow">for</span> (i = 0; i <= n; i++)</div> |
| <div class="line"><a name="l00091"></a><span class="lineno"> 91</span>  {</div> |
| <div class="line"><a name="l00092"></a><span class="lineno"> 92</span>  p[i] = i;</div> |
| <div class="line"><a name="l00093"></a><span class="lineno"> 93</span>  }</div> |
| <div class="line"><a name="l00094"></a><span class="lineno"> 94</span> </div> |
| <div class="line"><a name="l00095"></a><span class="lineno"> 95</span>  <span class="keywordflow">for</span> (j = 1; j <= m; j++)</div> |
| <div class="line"><a name="l00096"></a><span class="lineno"> 96</span>  {</div> |
| <div class="line"><a name="l00097"></a><span class="lineno"> 97</span>  t_j = other[j - 1];</div> |
| <div class="line"><a name="l00098"></a><span class="lineno"> 98</span>  d[0] = j;</div> |
| <div class="line"><a name="l00099"></a><span class="lineno"> 99</span> </div> |
| <div class="line"><a name="l00100"></a><span class="lineno"> 100</span>  <span class="keywordflow">for</span> (i = 1; i <= n; i++)</div> |
| <div class="line"><a name="l00101"></a><span class="lineno"> 101</span>  {</div> |
| <div class="line"><a name="l00102"></a><span class="lineno"> 102</span>  cost = sa[i - 1] == t_j ? 0 : 1;</div> |
| <div class="line"><a name="l00103"></a><span class="lineno"> 103</span>  <span class="comment">// minimum of cell to the left+1, to the top+1, diagonally left and up +cost</span></div> |
| <div class="line"><a name="l00104"></a><span class="lineno"> 104</span>  d[i] = Math.Min(Math.Min(d[i - 1] + 1, p[i] + 1), p[i - 1] + cost);</div> |
| <div class="line"><a name="l00105"></a><span class="lineno"> 105</span>  }</div> |
| <div class="line"><a name="l00106"></a><span class="lineno"> 106</span> </div> |
| <div class="line"><a name="l00107"></a><span class="lineno"> 107</span>  <span class="comment">// copy current distance counts to 'previous row' distance counts</span></div> |
| <div class="line"><a name="l00108"></a><span class="lineno"> 108</span>  _d = p;</div> |
| <div class="line"><a name="l00109"></a><span class="lineno"> 109</span>  p = d;</div> |
| <div class="line"><a name="l00110"></a><span class="lineno"> 110</span>  d = _d;</div> |
| <div class="line"><a name="l00111"></a><span class="lineno"> 111</span>  }</div> |
| <div class="line"><a name="l00112"></a><span class="lineno"> 112</span> </div> |
| <div class="line"><a name="l00113"></a><span class="lineno"> 113</span>  <span class="comment">// our last action in the above loop was to switch d and p, so p now</span></div> |
| <div class="line"><a name="l00114"></a><span class="lineno"> 114</span>  <span class="comment">// actually has the most recent cost counts</span></div> |
| <div class="line"><a name="l00115"></a><span class="lineno"> 115</span>  <span class="keywordflow">return</span> 1.0f - ((float)p[n] / Math.Max(other.Length, sa.Length));</div> |
| <div class="line"><a name="l00116"></a><span class="lineno"> 116</span>  }</div> |
| <div class="line"><a name="l00117"></a><span class="lineno"> 117</span>  }</div> |
| <div class="line"><a name="l00118"></a><span class="lineno"> 118</span> }</div> |
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