Angele Z.

lib/recursive-methods.rb

@@ -1,49 +1,87 @@
+require 'pry'
 # 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.new("BAD") if n < 0 
+  return 1 if n == 0
+  return n if n == 1
+  return n * factorial(n-1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def reverse(s)
-    raise NotImplementedError, "Method not implemented"
+  return s if s.length <= 1
+  return reverse(s[1..-1]) + s[0]
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n)
+# Space complexity: O(n)
+def reverse_inplace(s, i = 0)
+  return s if i == s.length / 2
+  s[i], s[s.length - i - 1] = s[s.length - i - 1], s[i]
+  s = reverse_inplace(s, i += 1)
 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 <= 0
+  return 2 + bunny(n - 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2) since using .length?
+# Space complexity: O(n)
 def nested(s)
-    raise NotImplementedError, "Method not implemented"
+  return false if s.length % 2 != 0
+  return true if s == ""
+  return true if s == "()"
+  center_l = s.length / 2 - 1
+  center_r = center_l + 1
+  if s[center_l] + s[center_r] != "()"
+    return false
+  else
+    next_string = s[center_l - 1] + s[center_r + 1]
+  end
+  return nested(next_string)
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def search(array, value)
-    raise NotImplementedError, "Method not implemented"
+  return false if array.empty?
+  return true if array[0] == value
+  new_array = array[1..-1]
+  return search(array[1..-1], value)
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def is_palindrome(s)
-    raise NotImplementedError, "Method not implemented"
+  return true if s.length <= 1
+  if s[0] != s[-1]
+    return false
+  else
+    next_string = s[1..-2]
+  end
+  return is_palindrome(next_string)
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2) since it uses .length in each loop?
+# Space complexity: O(n)
 def digit_match(n, m)
-    raise NotImplementedError, "Method not implemented"
-end
+  n = n.to_s
+  m = m.to_s
+  return 0 if n == nil || m == nil || n.length == 0 || m.length == 0
+  match = n[-1] == m[-1]
+  if match && (n.length == 1 || m.length == 1)
+    return 1 
+  elsif !match && (n.length == 1 || m.length == 1)
+    return 0
+  elsif !match
+    return 0 + digit_match(n[0..-2].to_i, m[0..-2].to_i)
+  else
+    return 1 + digit_match(n[0..-2].to_i, m[0..-2].to_i)
+  end
+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"
@@ -224,15 +224,15 @@
   end
 
   it "will return true when looking for something in the array" do
-  # Arrange
-  item = "a"
-  array = ["b", "c", "a"]
+    # Arrange
+    item = "a"
+    array = ["b", "c", "a"]
 
-  # Act
-  answer = search(array, item)
+    # Act
+    answer = search(array, item)
 
-  # Assert
-  expect(answer).must_equal true
+    # Assert
+    expect(answer).must_equal true
   end
 
   it "will return false when looking for something not in the array" do
@@ -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