new file: Text/longest_common_prefix.rb

Author: trizen

README.md

@@ -17,5 +17,6 @@ A small collection of day-to-day Ruby scripts used in solving problems or in imp
     * [Roman numerals decode](./Math/roman_numerals_decode.rb)
     * [Roman numerals encode](./Math/roman_numerals_encode.rb)
 * Text
+    * [Longest common prefix](./Text/longest_common_prefix.rb)
     * [Smart word wrap](./Text/smart_word_wrap.rb)
     * [Smart word wrap lazy](./Text/smart_word_wrap_lazy.rb)

Text/longest_common_prefix.rb

@@ -0,0 +1,51 @@
+#!/usr/bin/ruby
+
+# Find the longest common prefix, given a list of words.
+
+def find_common_prefix(hash, acc)
+
+    return acc if !hash
+
+    if (hash.size == 1)
+        key   = hash.keys[0]
+        value = hash.values[0]
+        return find_common_prefix(value, acc + key)
+    end
+
+    return acc
+end
+
+def lcp(strs)
+    hash = {}
+
+    for str in (strs.sort_by {|t| t.size })
+        ref = hash
+        return "" if str.empty?
+        for char in (str.chars)
+            if (ref.has_key?(char))
+                ref = ref[char]
+                break if (ref.size == 0)
+            else
+                ref = (ref[char] = {})
+            end
+        end
+    end
+
+    return find_common_prefix(hash, '')
+end
+
+tests = [
+  ["interspecies","interstellar","interstate"],
+  ["throne","throne"],
+  ["throne","dungeon"],
+  ["throne","","throne"],
+  ["cheese"],
+  [""],
+  [],
+  ["prefix","suffix"],
+  ["foo","foobar"]
+]
+
+for test in tests
+    puts "lcp(#{test}) = \"#{lcp(test)}\""
+end