Leaves - Emily V

lib/recursive-methods.rb

@@ -1,49 +1,67 @@
 # Authoring recursive algorithms. Add comments including time and space complexity for each method.
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def factorial(n)
-    raise NotImplementedError, "Method not implemented"
+  raise ArgumentError if n < 0
+  return 1 if n == 0
+  return n * factorial(n - 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def reverse(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n), where n is the length of the string
+# Space complexity: O(n), where n is the length of the string
+def reverse(s, pointer = s.length - 1)
+  return s if s == ""
+  return s[pointer] if pointer == 0
+  return s[pointer] + reverse(s, pointer - 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n), where n is the length of the string. (More precisely, n/2)
+# Space complexity: O(n), where n is the length of the string. (More precisely, n/2)
+def reverse_inplace(s, start = 0, finish = s.length - 1)
+  return s[start] if start == finish 
+  return "" if start > finish
+  return s[finish] + reverse_inplace(s, start + 1, finish - 1) + s[start] 
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def bunny(n)
-    raise NotImplementedError, "Method not implemented"
+  return 0 if n < 1
+  return 2 if n == 1
+  return 2 + bunny(n - 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def nested(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n), where n is the length of the string
+# Space complexity: O(n), where n is the length of the string
+def nested(s, parens_counter = 0, pointer = 0)
+  return false if parens_counter < 0
+  return true if pointer == s.length && parens_counter == 0
+  return false if pointer == s.length && parens_counter != 0
+  return nested(s, parens_counter + 1, pointer + 1) if s[pointer] == "("
+  return nested(s, parens_counter - 1, pointer + 1) if s[pointer] == ")"
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def search(array, value)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n), where n is the length of the string
+# Space complexity: O(n), where n is the length of the string
+def search(array, value, pointer = 0)
+  return false if pointer == array.length
+  return true if array[pointer] == value
+  return search(array, value, pointer + 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def is_palindrome(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n), where n is the length of the string (More precisely, n/2)
+# Space complexity: O(n), where n is the length of the string (More precisely, n/2)
+def is_palindrome(s, length = s.length, pointer = 0)
+  return true if pointer > length / 2
+  return false if s[pointer] != s[length - 1 - pointer]
+  return is_palindrome(s, length, pointer + 1) if s[pointer] == s[length - 1 - pointer]
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def digit_match(n, m)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n), where n is the length of the shorter string
+# Space complexity: O(n), where n is the length of the shorter string
+def digit_match(n, m, pointer = -1, matches = 0)
+  return matches if (pointer).abs > n.to_s.length || (pointer).abs > m.to_s.length
+  return digit_match(n, m, pointer - 1, matches + 1) if n.to_s[pointer] == m.to_s[pointer]
+  return digit_match(n, m, pointer - 1, matches) if n.to_s[pointer] != m.to_s[pointer]
 end

test/recursion_writing_test.rb

@@ -33,12 +33,12 @@
 
     # Act-Assert
     expect {
-      answer = factorial(num)
+      factorial(num)
     }.must_raise ArgumentError
   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 = ""
@@ -295,7 +295,7 @@
   end
 end
 
-xdescribe "digit_match" do
+describe "digit_match" do
   it "returns 4 for 1072503891 and 62530841" do
     # Arrange
     num1 = 1072503891