branches - vi

lib/recursive-methods.rb

@@ -1,49 +1,100 @@
 # Authoring recursive algorithms. Add comments including time and space complexity for each method.
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2)
+# Space complexity: O(n^2)
 def factorial(n)
-    raise NotImplementedError, "Method not implemented"
+  if n < 0 
+    raise ArgumentError
+  elsif n <= 1 
+    return 1 
+  else
+    return n * factorial(n - 1)
+  end 
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def reverse(s)
-    raise NotImplementedError, "Method not implemented"
-end
+  reversed_string = ""
+  if s.length >= 1 
+    reversed_string = reverse(s[1..-1])
+    reversed_string += s[0]
+  else 
+    return reversed_string
+  end
+end 
 
-# Time complexity: ?
-# Space complexity: ?
-def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n)
+# Space complexity: O(1)
+def reverse_inplace(s, i = 0, j = -1)
+  n = s.length 
+  if i == n / 2 
+    return s 
+  else 
+    letter = s[i]
+    s[i] = s[j]
+    s[j] = letter 
+    reverse_inplace(s, i + 1, j - 1)
+  end 
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def bunny(n)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n)
+# Space complexity: O(n)
+def bunny(n, ears = 0)
+  if ears == n + n 
+    return ears
+  else
+    ears += n
+    bunny(n, ears)
+  end 
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def nested(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n)
+# Space complexity: O(n)
+def nested(s, low = 0, high = (s.length - 1))
+  if s.length.odd?
+    return false 
+  elsif low < high 
+    if s[low] != "(" && s[high] != ")"
+      return false 
+    end 
+    return nested(s, low + 1, high - 1)
+  else 
+    return true 
+  end 
 end
 
-# Time complexity: ?
+# Time complexity: O(n)
 # Space complexity: ?
 def search(array, value)
-    raise NotImplementedError, "Method not implemented"
-end
+  new_array_minus_one = 0..-2
 
-# Time complexity: ?
-# Space complexity: ?
-def is_palindrome(s)
-    raise NotImplementedError, "Method not implemented"
+  if array.empty?  
+    return false 
+  elsif array[-1] == value
+    return true 
+  else 
+    search(array[new_array_minus_one], value)
+  end 
+end 
+
+# Time complexity: O(n)
+# Space complexity: O(1) 
+def is_palindrome(s, i = 0, j = -1)
+  n = s.length 
+
+  if i >= s.length + j
+    return true
+  elsif
+    s[i] != s[j]
+    return false
+  elsif s[i] == s[j]
+    is_palindrome(s, i + 1, j - 1)
+  end 
 end
 
 # Time complexity: ?
 # Space complexity: ?
 def digit_match(n, m)
-    raise NotImplementedError, "Method not implemented"
+
 end

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"
@@ -129,7 +129,7 @@
   end
 end
 
-xdescribe "bunny" do
+describe "bunny" do
   it "returns 0 for 0 bunnies" do
     # Arrange
     count = 0
@@ -164,7 +164,7 @@
   end
 end
 
-xdescribe "nested" do
+describe "nested" do
   it "will return true for empystring" do
     # Arrange
     string = ""
@@ -210,7 +210,7 @@
   end
 end
 
-xdescribe "search" do
+describe "search" do
   it "will return false for empty array" do
     # Arrange
     item = "a"
@@ -260,7 +260,7 @@
     end      
 end
 
-xdescribe "is_palindrome" do
+describe "is_palindrome" do
   it "will return true for emptystring" do
     # Arrange
     string = ""