diff --git a/lib/cw.rb b/lib/cw.rb
new file mode 100644
index 0000000..a2d17b4
--- /dev/null
+++ b/lib/cw.rb
@@ -0,0 +1,28 @@
+def reverse_inplace(s)
+  #  accepts a string as a parameter and then reverses the string IN PLACE using a recursive algorithm.
+  
+  # helper method, which will be called as a recursive function
+  def swap(s, left_index, right_index)
+    temp = s[left_index] 
+    s[left_index] = s[right_index]
+    s[right_index] = temp
+    return s
+  end
+  
+  left_index = 0
+  right_index = s.length - 1
+  
+  while left_index < right_index
+    s = swap(s, left_index, right_index)
+    left_index += 1
+    right_index -= 1
+  end
+  
+  return s
+end
+
+
+
+s = "super awesome"
+p reverse_inplace(s)
+
diff --git a/lib/recursive-methods.rb b/lib/recursive-methods.rb
index fbf6faa..e4148ce 100644
--- a/lib/recursive-methods.rb
+++ b/lib/recursive-methods.rb
@@ -1,49 +1,258 @@
 # Authoring recursive algorithms. Add comments including time and space complexity for each method.
+# https://github.com/stupendousC/recursion-writing
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def factorial(n)
-    raise NotImplementedError, "Method not implemented"
+  if (n == 1) || (n == 0)
+    return 1
+  elsif n > 1
+    return n * factorial(n-1)
+  else
+    raise ArgumentError, "argument must be >= 0"
+  end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2) b/c line 24 made a new string O(n) * recursing O(n) times
+# Space complexity: O(n^2) b/c line 24 made a new string O(n) * recursing O(n) times
 def reverse(s)
-    raise NotImplementedError, "Method not implemented"
+  # accepts a string and returns the reverse of the string by reversing all letters and all words in the string
+  # ex: reverse("hello world") will convert the input string to "dlrow olleh"
+  if s.length <= 1
+    return s 
+  else
+    return s[-1] + reverse(s[1...-1]) + s[0]
+  end
+  
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+  #  accepts a string as a parameter and then reverses the string IN PLACE using a recursive algorithm.
+  left_index = 0
+  right_index = s.length - 1
+  
+  swap(s, left_index, right_index)
+  
+  return s
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# recursive fcn to be used inside reverse_inplace()
+def swap(s, left_index, right_index)
+  if left_index >= right_index
+    return 
+  else
+    temp = s[left_index] 
+    s[left_index] = s[right_index]
+    s[right_index] = temp
+    left_index += 1
+    right_index -= 1
+    swap(s, left_index, right_index)
+  end
+end
+
+
+# Time complexity: O(n)
+# Space complexity: O(n)
 def bunny(n)
-    raise NotImplementedError, "Method not implemented"
+  #   N represents a number of bunnies and each bunny has two big floppy ears. We want to compute the total number of ears across all the bunnies recursively (without loops or multiplication).
+  if n == 0
+    # base case: no bunnies left
+    return 0
+  elsif n >= 1
+    # recurse
+    return 2 + bunny(n-1)
+  else
+    # no negative bunnies
+    raise ArgumentError
+  end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2) b/c line 109 is O(n) for making new array, x O(n) recursive steps
+# Space complexity: O(n^2)?
 def nested(s)
-    raise NotImplementedError, "Method not implemented"
+  # puts "\nTESTING ON #{s}"
+  
+  # read from front until ( is found, return false if ) instead
+  i = 0
+  left_paren_found = false
+  while s[i] && left_paren_found==false
+    if s[i] == ")"
+      # puts "NOPE"
+      return false
+    elsif s[i] != "("
+      i += 1
+    else  
+      # puts "\tfound ( at index #{i}"
+      left_paren_found = true
+    end
+  end
+  
+  # read from back until ) is found, return false if ( instead
+  j = s.length-1
+  right_paren_found = false
+  while s[j] && right_paren_found==false
+    if s[j] == "("
+      # puts "BUSTED"
+      return false
+    elsif s[j] != ")"
+      j -= 1
+    else  
+      # puts "\tfound ) at index #{j}"
+      right_paren_found = true
+    end
+  end
+  
+  if (right_paren_found && left_paren_found) && (i < j)
+    # puts "recursion..."
+    return nested(s[i+1...j])
+  elsif !right_paren_found && !left_paren_found
+    return true
+  else
+    return false
+  end
+end
+
+### Chris says... 
+# This is only tangentially recursive, you have a lot of nested loop sand if-else blocks.
+
+def nested_Chris_inefficient(s)
+  return true if s.empty?
+  return false unless s[0] == "(" && s[-1] == ")"
+  return nested_Chris_inefficient(s[1..-2])   ### This makes it O(n)*O(n)
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def search(array, value)
-    raise NotImplementedError, "Method not implemented"
+def nested_Chris(s, i=0, j=s.length-1)
+  # O(n) time, O(n) space
+  # puts "looking at #{s[i..j]}, i=#{i} and j=#{j}"
+  return false if s.length % 2 == 1
+  
+  while i < j
+    return false unless s[i] == "(" && s[j] == ")"
+    return nested_Chris(s, i+1, j-1)  
+  end
+  
+  return true
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# s = "(())"
+# p nested_Chris_inefficient(s)
+# p nested_Chris(s)
+
+# Time complexity: O(n)
+# Space complexity: O(n)
+def search(array, value, i=0)
+  # accepts an unsorted array of integers and an integer value to find and then 
+  # returns true if the value if found in the unsorted array and false otherwise. 
+  if array.empty?
+    return false
+  end
+  if array[i] == value
+    return true
+  elsif array[i+1]
+    return search(array, value, i+1)
+  else 
+    return false
+  end
+  
+end
+
+# Time complexity: O(n^2) b/c O(n) for making new string * O(n) recursive steps
+# Space complexity: O(n^2)
 def is_palindrome(s)
-    raise NotImplementedError, "Method not implemented"
+  if (s.length == 0) || (s.length == 1)
+    return true
+  elsif s[0] == s[-1]
+    return is_palindrome(s[1...-1])
+  else
+    return false
+  end
+end
+
+def is_palindrome_better(s, i=0, j=s.length-1)
+  # O(n) time & space
+  while i < j
+    if s[i] == s[j]
+      return is_palindrome_better(s, i+1, j-1)
+    else
+      return false
+    end
+  end
+  
+  return true
 end
 
-# Time complexity: ?
-# Space complexity: ?
+
+# Time complexity: O(n), where n is the longer number
+# Space complexity: O(n)
 def digit_match(n, m)
-    raise NotImplementedError, "Method not implemented"
-end
\ No newline at end of file
+  # puts "digit_matching #{n} vs #{m}"
+  # puts "comparing #{n%10} vs #{m%10}"
+  
+  if n>9 && m>9
+    # recurse-able condition
+    if n%10 == m%10
+      return 1 + digit_match(n/10,m/10)
+    else
+      return 0 + digit_match(n/10, m/10)
+    end
+    
+  else
+    # no need to recurse, n and/or m already on single digits
+    if n%10 == m%10
+      return 1
+    else
+      return 0
+    end
+  end  
+end
+
+### can also treat n and m as strings and iter/compare from index -1
+def digit_match_str(n, m, i = -1)
+  s1 = n.to_s
+  s2 = m.to_s
+  
+  if (!s1[i]) || (!s2[i])
+    return 0
+  else
+    if s1[i] == s2[i]
+      return 1 + digit_match_str(s1,s2,i-1)
+    else
+      return 0 + digit_match_str(s1,s2,i-1)
+    end
+  end
+  
+end
+
+# n= 123451
+# m = 65431
+# p digit_match_str(n,m)
+
+
+# Added Fun
+# Time complexity: O(2^n), 2^n leaves
+# Space complexity: O(n) per Chris
+def fib(n)
+  # returns the nth fibonacci number
+  # e.g. fib(4) = (0 1 1 2 3) should return 3
+  # Try it with a large number (> 100), what do you notice happening?
+  # it got a lot slower as n increases, really noticeable around n=40
+  
+  if n == 0
+    return 0
+  elsif n == 1
+    return 1
+  else
+    # generate fib seq up to the n-th index place
+    return fib(n-1) + fib(n-2)
+  end
+end
+
+### to see fib(n) in action, uncomment chunk below
+# n = 0
+# while n < 200
+#   puts "\n\nn = #{n}"
+#   p fib(n)
+#   n+= 1
+# end
\ No newline at end of file
diff --git a/test/recursion_writing_test.rb b/test/recursion_writing_test.rb
index 820810e..ee7e97c 100644
--- a/test/recursion_writing_test.rb
+++ b/test/recursion_writing_test.rb
@@ -7,352 +7,352 @@
   it "will find the factorial of 0" do
     # Arrange
     num = 0
-
+    
     # Act
     answer = factorial(num)
-
+    
     # Assert
     expect(answer).must_equal 1
   end
-
+  
   it "will find the factorial of 5" do
     # Arrange
     num = 5
-
+    
     # Act
     answer = factorial(num)
-
+    
     # Assert
     expect(answer).must_equal 5*4*3*2*1
-
+    
   end
-
+  
   it "will raise an ArgumentError if given a number not >= 0" do
     # Arrange
     num = -1
-
+    
     # Act-Assert
     expect {
-      answer = factorial(num)
-    }.must_raise ArgumentError
-  end
+    answer = factorial(num)
+  }.must_raise ArgumentError
+end
 end
 
-xdescribe "reverse" do
+describe "reverse" do
   it "will reverse 'cat'" do
     # Arrange
     string = "cat"
-
+    
     # Act
     answer = reverse(string)
-
+    
     # Assert
     expect(answer).must_equal "tac"
   end
-
+  
   it "will reverse 'a'" do
     # Arrange
     string = "a"
-
+    
     # Act
     answer = reverse(string)
-
+    
     # Assert
     expect(answer).must_equal "a"
   end
-
+  
   it "will reverse empty string " do
     # Arrange
     string = ""
-
+    
     # Act
     answer = reverse(string)
-
+    
     # Assert
     expect(answer).must_equal ""
   end
   it "will reverse 'apple'" do
     # Arrange
     string = "apple"
-
+    
     # Act
     answer = reverse(string)
-
+    
     # Assert
     expect(answer).must_equal "elppa"
   end
 end
 
 
-xdescribe "reverse_in_place" do
+describe "reverse_in_place" do
   it "will reverse 'cat'" do
     # Arrange
     string = "cat"
-
+    
     # Act
     answer = reverse_inplace(string)
-
+    
     # Assert
     expect(answer).must_equal "tac"
   end
-
+  
   it "will reverse 'a'" do
     # Arrange
     string = "a"
-
+    
     # Act
     answer = reverse_inplace(string)
-
+    
     # Assert
     expect(answer).must_equal "a"
   end
-
+  
   it "will reverse empty string " do
     # Arrange
     string = ""
-
+    
     # Act
     answer = reverse_inplace(string)
-
+    
     # Assert
     expect(answer).must_equal ""
   end
   it "will reverse 'apple'" do
     # Arrange
     string = "apple"
-
+    
     # Act
     answer = reverse_inplace(string)
-
+    
     # Assert
     expect(answer).must_equal "elppa"
   end
 end
 
-xdescribe "bunny" do
+describe "bunny" do
   it "returns 0 for 0 bunnies" do
     # Arrange
     count = 0
-
+    
     # Act
     answer = bunny(count)
-
+    
     # Assert
     expect(answer).must_equal 0
   end
-
+  
   it "returns 2 for 1 bunny" do
     # Arrange
     count = 1
-
+    
     # Act
     answer = bunny(count)
-
+    
     # Assert
     expect(answer).must_equal 2
   end
-
+  
   it "returns 100 for 50 bunnies" do
     # Arrange
     count = 50
-
+    
     # Act
     answer = bunny(count)
-
+    
     # Assert
     expect(answer).must_equal 100
   end
 end
 
-xdescribe "nested" do
+describe "nested" do
   it "will return true for empystring" do
     # Arrange
     string = ""
-
+    
     # Act
     answer = nested(string)
-
+    
     # Assert
     expect(answer).must_equal true
   end
-
+  
   it "will return true for a nested series of parens" do
     # Arrange
     string = "((()))"
-
+    
     # Act
     answer = nested(string)
-
+    
     # Assert
     expect(answer).must_equal true
   end
-
+  
   it "will return false for a nested series of parens" do
     # Arrange
     string = "(()))"
-
+    
     # Act
     answer = nested(string)
-
+    
     # Assert
     expect(answer).must_equal false
   end
-
+  
   it "will return false for an even length improperly nested series of parens" do
     # Arrange
     string = "(())))"
-
+    
     # Act
     answer = nested(string)
-
+    
     # Assert
     expect(answer).must_equal false
   end
 end
 
-xdescribe "search" do
+describe "search" do
   it "will return false for empty array" do
     # Arrange
     item = "a"
     array = []
-
+    
     # Act
     answer = search(array, item)
-
+    
     # Assert
     expect(answer).must_equal false
   end
-
+  
   it "will return true when looking for something in the array" do
-  # Arrange
-  item = "a"
-  array = ["b", "c", "a"]
-
-  # Act
-  answer = search(array, item)
-
-  # Assert
-  expect(answer).must_equal true
+    # Arrange
+    item = "a"
+    array = ["b", "c", "a"]
+    
+    # Act
+    answer = search(array, item)
+    
+    # Assert
+    expect(answer).must_equal true
   end
-
+  
   it "will return false when looking for something not in the array" do
     # Arrange
     item = "x"
     array = ["b", "c", "a"]
-  
+    
     # Act
     answer = search(array, item)
-  
+    
     # Assert
     expect(answer).must_equal false
-    end
-
-    it "will return true when finding something at the front of the array" do
-      # Arrange
-      item = "b"
-      array = ["b", "c", "a"]
+  end
+  
+  it "will return true when finding something at the front of the array" do
+    # Arrange
+    item = "b"
+    array = ["b", "c", "a"]
     
-      # Act
-      answer = search(array, item)
+    # Act
+    answer = search(array, item)
     
-      # Assert
-      expect(answer).must_equal true
-    end      
+    # Assert
+    expect(answer).must_equal true
+  end      
 end
 
-xdescribe "is_palindrome" do
+describe "is_palindrome" do
   it "will return true for emptystring" do
     # Arrange
     string = ""
-
+    
     # Act
     answer = is_palindrome(string)
-
+    
     # Assert
     expect(answer).must_equal true
   end
-
+  
   it "will return true for a palindrome" do
     # Arrange
     string = "racecar"
-
+    
     # Act
     answer = is_palindrome(string)
-
+    
     # Assert
     expect(answer).must_equal true
   end
-
+  
   it "will return false for a nonpalindrome" do
     # Arrange
     string = "raecar"
-
+    
     # Act
     answer = is_palindrome(string)
-
+    
     # Assert
     expect(answer).must_equal false
   end
 end
 
-xdescribe "digit_match" do
+describe "digit_match" do
   it "returns 4 for 1072503891 and 62530841" do
     # Arrange
     num1 = 1072503891
     num2 = 62530841
-
+    
     # Act
     answer = digit_match(num1, num2)
-
-     # Assert
-     expect(answer).must_equal 4
+    
+    # Assert
+    expect(answer).must_equal 4
   end
-
+  
   it "returns 0 for nonmatching numbers" do
     # Arrange
     num1 = 0
     num2 = 62530841
-
+    
     # Act
     answer = digit_match(num1, num2)
-
-     # Assert
-     expect(answer).must_equal 0
+    
+    # Assert
+    expect(answer).must_equal 0
   end
-
+  
   it "returns 3 for 841 and 62530841" do
     # Arrange
     num1 = 841
     num2 = 62530841
-
+    
     # Act
     answer = digit_match(num1, num2)
-
-     # Assert
-     expect(answer).must_equal 3
+    
+    # Assert
+    expect(answer).must_equal 3
   end
   
   it "returns 1 for (0, 0)" do
     # Arrange
     num1 = 0
     num2 = 0
-
+    
     # Act
     answer = digit_match(num1, num2)
-
-     # Assert
-     expect(answer).must_equal 1
+    
+    # Assert
+    expect(answer).must_equal 1
   end
   
   it "returns 1 for (10, 20)" do
     # Arrange
     num1 = 10
     num2 = 20
-
+    
     # Act
     answer = digit_match(num1, num2)
-
-     # Assert
-     expect(answer).must_equal 1
+    
+    # Assert
+    expect(answer).must_equal 1
   end
 end