reverse sentence MS

lib/reverse_sentence.rb

@@ -1,4 +1,52 @@
 # A method to reverse the words in a sentence, in place.
 def reverse_sentence(my_sentence)
-  raise NotImplementedError
+  def reverse_sentence(sentence)
+  return nil if sentence.nil?
+
+  finish = nil
+  start = nil
+  on_first_word = true
+
+  is_finding_whitespace = sentence[-1] == ' '
+
+  (sentence.length - 1).downto(0) do |current_index|
+    current_char = sentence[current_index]
+
+    if is_finding_whitespace
+      if finish.nil? && current_char == ' '
+        finish = current_index
+      end
+
+      if start.nil? && sentence[current_index - 1] != ' '
+        start = current_index
+      end
+    else
+      # a word
+      if finish.nil? && current_char != ' '
+        finish = current_index
+      end
+
+      if start.nil? && sentence[current_index - 1] == ' '
+        start = current_index
+      end
+    end
+
+    if start.nil? && current_index == 0
+      start = current_index
+    end
+
+    if start && finish
+      if on_first_word
+        on_first_word = false
+      else
+        word = sentence.slice!(start..finish)
+        sentence << word
+      end
+
+      start = nil
+      finish = nil
+      is_finding_whitespace = !is_finding_whitespace
+    end
+  end
+end
 end