Earth - Lina

lib/recursive-methods.rb

@@ -1,45 +1,86 @@
 # 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
+
+    if n == 0 #base case
+        return 1
+    else
+        return n * factorial(n-1)
+    end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2)
+# Space complexity: O(n^2)
 def reverse(s)
-    raise NotImplementedError, "Method not implemented"
+    if s.length <= 1
+        return s
+    else
+        return s[-1] + reverse(s[1..-2]) + s[0]
+    end
 end
 
+
+
 # Time complexity: ?
 # Space complexity: ?
 def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+    if s.length <= 1
+        return s
+    else
+        return reverse_inplace(s[1..-1]) + s[0]
+    end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def bunny(n)
-    raise NotImplementedError, "Method not implemented"
+    if n == 0
+        return 0
+    else
+        return 2 + bunny(n-1)
+    end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2)
+# Space complexity: O(n^2)
 def nested(s)
-    raise NotImplementedError, "Method not implemented"
+    if s.empty?
+        return true
+    elsif s[0] == s[-1]
+        return false
+    else
+        return nested(s[1..-2])
+    end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2)
+# Space complexity: O(n^2)
 def search(array, value)
-    raise NotImplementedError, "Method not implemented"
+    if array.empty?
+        return false
+    elsif array[0] == value
+        return true
+    else
+        return search(array[1..-1], value)
+    end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2)
+# Space complexity: O(n^2)
 def is_palindrome(s)
-    raise NotImplementedError, "Method not implemented"
+    if s.length == 1 || s.empty?
+        return true
+    end
+
+    if s[0] == s[-1]
+        is_palindrome(s[1..-2])
+    else
+        return false
+    end
 end
 
 # Time complexity: ?

test/recursion_writing_test.rb

@@ -167,7 +167,7 @@
   end
 end
 
-xdescribe "nested" do
+describe "nested" do
   it "will return true for empystring" do
     # Arrange
     string = ""
@@ -213,7 +213,7 @@
   end
 end
 
-xdescribe "search" do
+describe "search" do
   it "will return false for empty array" do
     # Arrange
     item = "a"
@@ -263,7 +263,7 @@
     end      
 end
 
-xdescribe "is_palindrome" do
+describe "is_palindrome" do
   it "will return true for emptystring" do
     # Arrange
     string = ""
@@ -298,7 +298,7 @@
   end
 end
 
-xdescribe "digit_match" do
+describe "digit_match" do
   it "returns 4 for 1072503891 and 62530841" do
     # Arrange
     num1 = 1072503891