spellcheck challenge with tries

challenges/spellcheck.rb

@@ -0,0 +1,90 @@
+#!/usr/bin/env ruby
+
+# Spellchecker
+
+# Write a program that reads a large list of English words (e.g. from /usr/share/dict/words on a unix system) into memory, and then reads words from stdin, and prints either the best spelling suggestion, or "NO SUGGESTION" if no suggestion can be found. The program should print ">" as a prompt before reading each word, and should loop until killed.
+
+# Your solution should be faster than O(n) per word checked, where n is the length of the dictionary. That is to say, you can't scan the dictionary every time you want to spellcheck a word.
+
+# For example:
+
+# > sheeeeep
+# sheep
+# > peepple
+# people
+# > sheeple
+# NO SUGGESTION
+# The class of spelling mistakes to be corrected is as follows:
+
+# Case (upper/lower) errors: "inSIDE" => "inside"
+# Repeated letters: "jjoobbb" => "job"
+# Incorrect vowels: "weke" => "wake"
+# Any combination of the above types of error in a single word should be corrected (e.g. "CUNsperrICY" => "conspiracy").
+
+# If there are many possible corrections of an input word, your program can choose one in any way you like. It just has to be an English word that is a spelling correction of the input by the above rules.
+
+  class String
+
+    # ancient semitic languages had no vowels
+    # this variation also prevents serial duplicates
+    def to_sem
+      self.gsub(/[a e i o u y]+/,'').
+        split('').
+        inject('') do |m,x|
+          m << x if m[-1] != x
+          m
+        end
+    end
+
+    def to_sa
+      self.split('').map(&:to_sym)
+    end
+
+  end
+
+  class Trie
+    def initialize
+      @root = Hash.new
+    end
+
+    def build(stringy)
+      str = stringy.to_sem.to_sa
+      node = @root
+      str.each do |ch|
+        node[ch] ||= Hash.new
+        node = node[ch]
+      end
+      node[:end] = stringy
+    end
+
+    def find(stringy)
+      str = stringy.to_sem.to_sa
+      node = @root
+      str.each do |ch|
+        return nil unless node = node[ch]
+      end
+      node[:end]
+    end
+  end
+
+@dictionary = Trie.new
+file = ARGV[0] || "/usr/share/dict/words"
+
+if file == 'help'
+  puts "usage: spellcheck.rb [dictionary-file]"
+  exit
+end
+
+puts "building dictionary from #{file}"
+
+
+File.open(file).readlines.each do |x|
+  @dictionary.build(x.downcase.chomp)
+end
+
+loop do
+  print "> "
+  s = gets.chomp
+  puts @dictionary.find(s) || "NO SUGGESTION"
+end
+