Added levenshtein distance implementation.

levenshtein.py

@@ -0,0 +1,82 @@
+#   Copyright (C) 2008 by Albert Cervera i Areny
+#   albert@nan-tic.com
+#
+#   This program is free software; you can redistribute it and/or modify 
+#   it under the terms of the GNU General Public License as published by
+#   the Free Software Foundation; either version 2 of the License, or 
+#   (at your option) any later version. 
+#
+#   This program is distributed in the hope that it will be useful, 
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of 
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
+#   GNU General Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License 
+#   along with this program; if not, write to the
+#   Free Software Foundation, Inc.,
+#   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA. 
+
+class Levenshtein:
+
+	@staticmethod
+	def levenshtein( text1, text2 ):
+		d = []
+		# Should use an array instead..
+		for i in range(len(text1)):
+			d.append( [] )
+			for j in range(len(text1)):
+				d[i].append(0)
+
+		for i in range(len(text1)):
+			d[i][0] = i
+
+		for j in range(len(text2)):
+			d[0][j] = j
+
+		for i in range(len(text1)-1): 
+			for j in range(len(text2)-1):
+				ip = i+1
+				jp = j+1
+				if text1[ip] == text2[jp]:
+					cost = 0
+				else:
+					cost = 1
+
+				d[ip][jp] = min( 
+					d[ip-1][jp] + 1,      # deletion
+					d[ip][jp-1] + 1,      # insertion
+					d[ip-1][jp-1] + cost  # substitution
+				)
+		return d[len(text1)-1][len(text2)-1]
+
+#Pseudocode:
+#int LevenshteinDistance(char s[1..m], char t[1..n])
+	#// d is a table with m+1 rows and n+1 columns
+	#declare int d[0..m, 0..n]
+#
+	#for i from 0 to m
+		#d[i, 0] := i
+	#for j from 0 to n
+		#d[0, j] := j
+#
+	#for i from 1 to m
+		#for j from 1 to n
+		#{
+			#if s[i] = t[j] then 
+				#cost := 0
+			#else 
+				#cost := 1
+			#d[i, j] := minimum(
+				#d[i-1, j] + 1,     // deletion
+				#d[i, j-1] + 1,     // insertion
+				#d[i-1, j-1] + cost   // substitution
+			#)
+		#}
+	#return d[m, n]
+
+if __name__ == '__main__':
+	print Levenshtein.levenshtein( 'abc', 'abc' )
+	print Levenshtein.levenshtein( 'abcabc', 'abc' )
+	print Levenshtein.levenshtein( 'abcdef', 'abc' )
+	print Levenshtein.levenshtein( 'abcdef', 'bcd' )
+	print Levenshtein.levenshtein( 'bcdef', 'abc' )