From ee071ccc5ab76074c716c8309be1a9a02110a862 Mon Sep 17 00:00:00 2001
From: daniela sanchez <dnsanche@gmail.com>
Date: Wed, 13 Nov 2019 22:37:13 -0800
Subject: [PATCH] First 3 methods

---
 lib/recursive-methods.rb       | 47 ++++++++++++++++++++++++++--------
 test/recursion_writing_test.rb |  4 +--
 2 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/lib/recursive-methods.rb b/lib/recursive-methods.rb
index fbf6faa..1691179 100644
--- a/lib/recursive-methods.rb
+++ b/lib/recursive-methods.rb
@@ -1,21 +1,46 @@
 # Authoring recursive algorithms. Add comments including time and space complexity for each method.
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n), because of the size of the stack (number of methods that is accumulated in the stack to run)
+# Space complexity: O(n), because of the size of this stack
 def factorial(n)
-    raise NotImplementedError, "Method not implemented"
+  #Base Case
+  return 1 if n == 0
+  raise ArgumentError if n < 0
+
+  #Recursive Case
+  return n * factorial(n-1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def reverse(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n), it will iterate through all elements of string
+# Space complexity: O(1), it will always use same number of variables (i, j, memo)
+def reverse(s )  
+  i = 0
+  j = s.length - 1
+
+    while i < j
+      memo = s[i]
+      s[i] = s[j]
+      s[j] = memo
+      
+      i += 1
+      j -= 1
+    end
+    return s
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n) ~ n/2 as increasing and decreasing both pointer in same call
+# Space complexity: O(n), n/2 recursive calls,
+# because both pointers are moving each time the method is called
+def reverse_inplace(s, i = 0, j = s.length - 1)
+    #Base Case
+  return s if i >= j
+
+  #Recursive Case
+      memo = s[i]
+      s[i] = s[j]
+      s[j] = memo
+  return reverse_inplace(s, i + 1, j - 1)  
+
 end
 
 # Time complexity: ?
diff --git a/test/recursion_writing_test.rb b/test/recursion_writing_test.rb
index 820810e..63e3dbc 100644
--- a/test/recursion_writing_test.rb
+++ b/test/recursion_writing_test.rb
@@ -38,7 +38,7 @@
   end
 end
 
-xdescribe "reverse" do
+describe "reverse" do
   it "will reverse 'cat'" do
     # Arrange
     string = "cat"
@@ -84,7 +84,7 @@
 end
 
 
-xdescribe "reverse_in_place" do
+describe "reverse_in_place" do
   it "will reverse 'cat'" do
     # Arrange
     string = "cat"