diff --git a/lib/reverse_sentence.rb b/lib/reverse_sentence.rb
index 3fe7cac..bd403c3 100644
--- a/lib/reverse_sentence.rb
+++ b/lib/reverse_sentence.rb
@@ -1,6 +1,61 @@
 # A method to reverse the words in a sentence, in place.
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n ^2) because lines 47-55 contain a nested loop.
+# Space complexity: ? O(n) because of the empty_index_positions array from lines 33 - 38
+
+def swap_chars(arr, index_one, index_two)
+  tmp = arr[index_two]
+  arr[index_two] = arr[index_one]
+  arr[index_one] = tmp
+end
+
+def reverse_sub_str(array, start_position, end_position)
+  ((end_position - start_position + 1) / 2).times do
+    swap_chars(array, start_position, end_position)
+    start_position += 1
+    end_position -= 1
+  end 
+  return array
+end 
+
 def reverse_sentence(my_sentence)
-  raise NotImplementedError
+  
+  if my_sentence == ""
+    return ""
+  elsif my_sentence == nil
+    return nil 
+  end
+  
+  
+  i = 0
+  j = (my_sentence.length) -1 
+  reverse_sub_str(my_sentence, i, j)
+  
+  empty_index_positions = []
+  my_sentence.length.times do |i|
+    if my_sentence[i] == " "
+      empty_index_positions << i 
+    end 
+  end
+  
+  if empty_index_positions.length == 0 
+    i = 0
+    j = (my_sentence.length) -1 
+    reverse_sub_str(my_sentence, i, j)
+    return my_sentence
+  end
+  
+  empty_index_positions.length.times do |i|
+    if i == 0
+      reverse_sub_str(my_sentence, i, empty_index_positions[i] - 1)
+    else 
+      start_position = empty_index_positions[i - 1] + 1
+      end_position = empty_index_positions[i] - 1
+      reverse_sub_str(my_sentence, start_position, end_position)
+    end 
+  end 
+  
+  i = empty_index_positions[-1] + 1
+  j = my_sentence.length - 1
+  reverse_sub_str(my_sentence, i, j )
+  return my_sentence
 end
diff --git a/lib/sort_by_length.rb b/lib/sort_by_length.rb
index a5713ad..862d1f9 100644
--- a/lib/sort_by_length.rb
+++ b/lib/sort_by_length.rb
@@ -1,7 +1,30 @@
 # A method which will return an array of the words in the string
 #  sorted by the length of the word.
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n ^ 2)
+# Space complexity: ? O(n) because of splitting the string at the beginning of the method
+
+def swap(arr, index_one, index_two)
+  tmp = arr[index_two]
+  arr[index_two] = arr[index_one]
+  arr[index_one] = tmp
+end
+
+
 def sort_by_length(my_sentence)
-  raise NotImplementedError, "Method not implemented"
+  my_sentence = my_sentence.split 
+  
+  j = 0 # outer counter
+  my_sentence.length.times do
+    comparison_word = my_sentence[j]
+    for i in j...(my_sentence.length)
+      if my_sentence[i].length < comparison_word.length
+        puts my_sentence[i]
+        puts comparison_word
+        swap(my_sentence, i, j )
+        comparison_word = my_sentence[j]
+      end
+    end
+    j += 1
+  end
+  return my_sentence
 end
diff --git a/test/reverse_sentence_test.rb b/test/reverse_sentence_test.rb
index 346069b..02400d2 100644
--- a/test/reverse_sentence_test.rb
+++ b/test/reverse_sentence_test.rb
@@ -4,70 +4,70 @@
   describe "basic tests" do
     it "reverse a sentence with two words" do
       test_string = "hello, world"
-
+      
       reverse_sentence(test_string)
-
+      
       test_string.must_equal "world hello,"
     end
-
+    
     it "reverse a sentence with three words" do
       test_string = "Yoda is awesome!"
-
+      
       reverse_sentence(test_string)
-
+      
       test_string.must_equal "awesome! is Yoda"
     end
   end
-
+  
   # check for edge cases
   describe "edge cases" do
     # if it's a string parameter, check for empty
     it "reverse an empty sentence" do
       test_string = ""
-
+      
       reverse_sentence(test_string)
-
+      
       test_string.must_be_empty
     end
-
+    
     # if the parameter is an object, check for nil
     it "nil object passed to sentence reverse" do
       test_string = nil
-
+      
       reverse_sentence(test_string)
-
+      
       test_string.must_be_nil
     end
-
+    
     it "reverse a sentence with one word" do
       test_string = "world"
-
+      
       reverse_sentence(test_string)
-
+      
       test_string.must_equal "world"
     end
-
+    
     it "reverse a sentence with multiple words" do
       test_string = "I'm a better engineer today than I was yesterday."
-
+      
       reverse_sentence(test_string)
-
+      
       test_string.must_equal "yesterday. was I than today engineer better a I'm"
     end
-
+    
     it "reverse a sentence with multiple spaces between words" do
       test_string = "How  do  you   like     them      apples?"
-
+      
       reverse_sentence(test_string)
-
+      
       test_string.must_equal "apples?      them     like   you  do  How"
     end
-
+    
     it "reverse a sentence with preceeding and trailing white spaces" do
       test_string = "  I can do this!     "
-
+      
       reverse_sentence(test_string)
-
+      
       test_string.must_equal "     this! do can I  "
     end
   end