From eab59d2f7e02b31be0bf76981a45d6f2e5ba362b Mon Sep 17 00:00:00 2001
From: ligi <ligiso@gmail.com>
Date: Thu, 23 Nov 2017 23:33:22 +0800
Subject: [PATCH] fix RatcliffObershelpSimilarity at ("abab","ababab") case

---
 FuzzyString/RatcliffObershelpSimilarity.cs | 53 +++++++++++++++++++++-
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/FuzzyString/RatcliffObershelpSimilarity.cs b/FuzzyString/RatcliffObershelpSimilarity.cs
index 386340c..2453c4d 100644
--- a/FuzzyString/RatcliffObershelpSimilarity.cs
+++ b/FuzzyString/RatcliffObershelpSimilarity.cs
@@ -10,7 +10,56 @@ public static partial class ComparisonMetrics
     {
         public static double RatcliffObershelpSimilarity(this string source, string target)
         {
-            return (2 * Convert.ToDouble(source.Intersect(target).Count())) / (Convert.ToDouble(source.Length + target.Length));
+            var matchs = GetMatchQueue(source, target);
+            return 2.0 * matchs.Select(match => match.Length).Sum() / (source.Length + target.Length);
+        }
+
+        private static List<string> GetMatchQueue(string source, string target)
+        {
+            List<string> list = new List<string>();
+            var match = FrontMaxMatch(source, target);
+            if (match.Length > 0)
+            {
+                var frontSource = source.Substring(0, source.IndexOf(match));
+                var frontTarget = target.Substring(0, target.IndexOf(match));
+                var frontQueue = GetMatchQueue(frontSource, frontTarget);
+
+                var endSource = source.Substring(source.IndexOf(match) + match.Length);
+                var endTarget = target.Substring(target.IndexOf(match) + match.Length);
+                var endQueue = GetMatchQueue(endSource, endTarget);
+
+                list.Add(match);
+                list.AddRange(frontQueue);
+                list.AddRange(endQueue);
+                return list;
+            }
+            else
+            {
+                return list;
+            }
+        }
+
+        private static string FrontMaxMatch(string a, string b)
+        {
+            var index = 0;
+            var length = 0;
+
+            for (int i = 0; i < a.Length; i++)
+            {
+                Enumerable.Range(1, a.Length - i)
+                .ToList()
+                .ForEach
+                (len =>
+                {
+                    if (len > length && b.Contains(a.Substring(i, len)))
+                    {
+                        index = i;
+                        length = len;
+                    }
+                });
+            }
+
+            return a.Substring(index, length);
         }
     }
-}
+}
\ No newline at end of file