Add Levenshtein distance in C as part of String algorithms

Author: kanwei

History.txt

@@ -1,3 +1,7 @@
+=== Jan 3, 2009
+
+    * Levenshtein distance in C
+
 === April 3, 2009
 
 	* Finished C refactorization of SplayTree

Manifest

@@ -1,17 +1,23 @@
+History.txt
+Manifest
+README.markdown
+Rakefile
 algorithms.gemspec
 benchmarks/deque.rb
 benchmarks/sorts.rb
 benchmarks/treemaps.rb
+ext/algorithms/string/extconf.rb
+ext/algorithms/string/string.c
 ext/containers/deque/deque.c
 ext/containers/deque/extconf.rb
 ext/containers/rbtree_map/extconf.rb
 ext/containers/rbtree_map/rbtree.c
 ext/containers/splaytree_map/extconf.rb
 ext/containers/splaytree_map/splaytree.c
-History.txt
+lib/algorithms.rb
 lib/algorithms/search.rb
 lib/algorithms/sort.rb
-lib/algorithms.rb
+lib/algorithms/string.rb
 lib/containers/deque.rb
 lib/containers/heap.rb
 lib/containers/kd_tree.rb
@@ -22,20 +28,20 @@ lib/containers/splay_tree_map.rb
 lib/containers/stack.rb
 lib/containers/suffix_array.rb
 lib/containers/trie.rb
-Manifest
-Rakefile
-README.markdown
 spec/deque_gc_mark_spec.rb
 spec/deque_spec.rb
 spec/heap_spec.rb
+spec/kd_expected_out.txt
+spec/kd_test_in.txt
 spec/kd_tree_spec.rb
+spec/map_gc_mark_spec.rb
 spec/priority_queue_spec.rb
 spec/queue_spec.rb
-spec/rb_tree_map_gc_mark_spec.rb
 spec/rb_tree_map_spec.rb
 spec/search_spec.rb
 spec/sort_spec.rb
 spec/splay_tree_map_spec.rb
 spec/stack_spec.rb
+spec/string_spec.rb
 spec/suffix_array_spec.rb
 spec/trie_spec.rb

Rakefile

@@ -10,12 +10,6 @@ Echoe.new('algorithms') do |p|
   p.runtime_dependencies = []
 end
 
-task :default => :spec
-
-task :spec do
-  sh "spec spec/*.rb --color"
-end
-
 task :push do
   sh "git push"    # Rubyforge
   sh "git push --tags"    # Rubyforge

ext/algorithms/string/extconf.rb

@@ -0,0 +1,4 @@
+require 'mkmf'
+extension_name = "CString"
+dir_config(extension_name)
+create_makefile(extension_name)

ext/algorithms/string/string.c

@@ -0,0 +1,68 @@
+#include "ruby.h"
+
+int min(int a, int b, int c) {
+	int min = a;
+	if (b < min)
+		min = b;
+	if( c < min)
+		min = c;
+	return min;
+}
+
+int levenshtein_distance(VALUE str1, VALUE str2) {
+	int i, j, s1_len, s2_len, *d;
+	char * s = RSTRING(str1)->ptr;
+	char * t = RSTRING(str2)->ptr;
+	s1_len = RSTRING(str1)->len; 
+	s2_len = RSTRING(str2)->len;
+	
+	if (s1_len == 0) {
+		return s2_len;
+	} else if (s2_len == 0) {
+		return s1_len;
+	}
+	
+	// We need one extra col and row for the matrix for starting values
+	s1_len++;
+	s2_len++;
+	
+	d = malloc(sizeof(int) * (s1_len) * (s2_len));
+	
+	for (i = 0; i < s1_len; i++) {
+		d[i] = i; // d[i, 0] = i
+	}
+	for (j = 0; j < s2_len; j++) {
+		d[j*s1_len] = j; // d[0, j] = j
+	}
+	
+	for (i = 1; i < s1_len; i++) {
+		for (j = 1; j < s2_len; j++) {
+			if (s[i-1] == t[j-1]) {
+				d[j * s1_len + i] = d[(j-1) * s1_len + (i-1)];
+			} else {
+				d[j * s1_len + i] = min(
+					d[j * s1_len + (i-1)],
+					d[(j-1) * s1_len + i],
+					d[(j-1) * s1_len + (i-1)]
+				) + 1;
+			}
+		}
+	}
+	i = d[s1_len * s2_len -1];
+	free(d);
+	return i;
+}
+
+static VALUE lev_dist(VALUE self, VALUE str1, VALUE str2) {
+	return INT2FIX(levenshtein_distance( str1, str2 ));
+}
+
+static VALUE mAlgorithms;
+static VALUE mString;
+
+void Init_CString() {	
+	mAlgorithms = rb_define_module("Algorithms");
+	mString = rb_define_module_under(mAlgorithms, "String");
+	rb_define_singleton_method(mString, "levenshtein_dist", lev_dist, 2);
+}
+

lib/algorithms.rb

@@ -43,19 +43,16 @@
     - Shell sort            - Algorithms::Sort.shell_sort
     - Quicksort             - Algorithms::Sort.quicksort
     - Mergesort             - Algorithms::Sort.mergesort
+  * String algorithms
+    - Levenshtein distance  - Algorithms::String.levenshtein_dist
 =end
 
 module Algorithms; end
 module Containers; end
 
-begin
-  require 'CBst'
-  Containers::Bst = Containers::CBst
-rescue LoadError # C Version could not be found
-end
-
 require 'algorithms/search'
 require 'algorithms/sort'
+require 'algorithms/string'
 require 'containers/heap'
 require 'containers/stack'
 require 'containers/deque'

lib/algorithms/string.rb

@@ -0,0 +1,8 @@
+=begin rdoc
+    This module implements string algorithms. Documentation is provided for each algorithm.
+    
+=end
+
+begin
+  require 'CString'
+end

spec/string_spec.rb

@@ -0,0 +1,13 @@
+$: << File.join(File.expand_path(File.dirname(__FILE__)), '..', 'lib')
+require 'algorithms'
+
+describe "string algorithms" do
+  it "should do levenshtein distance" do    
+    Algorithms::String.levenshtein_dist("Hello", "Hel").should eql(2)
+    Algorithms::String.levenshtein_dist("Hello", "").should eql(5)
+    Algorithms::String.levenshtein_dist("", "Hello").should eql(5)
+    Algorithms::String.levenshtein_dist("Hello", "Hello").should eql(0)
+    Algorithms::String.levenshtein_dist("Hello", "ello").should eql(1)
+    Algorithms::String.levenshtein_dist("Hello", "Mello").should eql(1)
+  end
+end