Partial completed

lib/recursive-methods.rb

@@ -1,49 +1,89 @@
 # 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"
+  if n < 0
+    raise ArgumentError
+  elsif n <= 1 
+    return 1
+  else
+    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.empty? || s.length == 1
+    return s
+  else
+    s[-1] + reverse(s[1..-2]) + s[0]
+  end
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+# s = "bear"
+# reverse_in_place!(s)
+# s == "raeb"
+# "bear" => "reab" => "raeb"
+# reverse("bear") calls reverse("ea") calls reverse("")
+# reverse_in_place("bear")
+# calls r_i_p_helper("bear", 0)
+# calls r_i_p_helper("reab", 1)
+# calls r_i_p_helper("raeb", 2) -> returns "raeb"
+# r_i_p_helper("", 0) s.length = 0, idx = 0
+# ...("a", 0) s.length = 1, idx = 0
+# ...("raeb", 2) s.length = 4, idx = 2
+# ...("butter", 0) => ("rutteb", 1) => ("rettub", 2) ("rettub", 3) => return
+def reverse_in_place_helper(s, index)
+  if index == s.length / 2
+    return s
+  else
+    temp = s[index]
+    s[index] = s[s.length - index - 1]
+    s[s.length - index - 1] = temp
+    reverse_in_place_helper(s, index + 1)
+  end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
+def reverse_in_place(s)
+  reverse_in_place_helper(s, 0)
+end
+
+# 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: ?
 def nested(s)
-    raise NotImplementedError, "Method not implemented"
+  raise NotImplementedError, "Method not implemented"
 end
 
 # Time complexity: ?
 # Space complexity: ?
 def search(array, value)
-    raise NotImplementedError, "Method not implemented"
+  raise NotImplementedError, "Method not implemented"
 end
 
 # Time complexity: ?
 # Space complexity: ?
 def is_palindrome(s)
-    raise NotImplementedError, "Method not implemented"
+  raise NotImplementedError, "Method not implemented"
 end
 
 # Time complexity: ?
 # Space complexity: ?
 def digit_match(n, m)
-    raise NotImplementedError, "Method not implemented"
-end
+  raise NotImplementedError, "Method not implemented"
+end

test/recursion_writing_test.rb

@@ -1,11 +1,10 @@
-require 'minitest/autorun'
-require 'minitest/reporters'
+require "minitest/autorun"
+require "minitest/reporters"
 require "minitest/skip_dsl"
-require_relative '../lib/recursive-methods'
+require_relative "../lib/recursive-methods"
 
 Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
 
-
 describe "factorial" do
   it "will find the factorial of 0" do
     # Arrange
@@ -26,8 +25,7 @@
     answer = factorial(num)
 
     # Assert
-    expect(answer).must_equal 5*4*3*2*1
-
+    expect(answer).must_equal 5 * 4 * 3 * 2 * 1
   end
 
   it "will raise an ArgumentError if given a number not >= 0" do
@@ -86,14 +84,13 @@
   end
 end
 
-
 describe "reverse_in_place" do
   it "will reverse 'cat'" do
     # Arrange
     string = "cat"
 
     # Act
-    answer = reverse_inplace(string)
+    answer = reverse_in_place(string)
 
     # Assert
     expect(answer).must_equal "tac"
@@ -104,7 +101,7 @@
     string = "a"
 
     # Act
-    answer = reverse_inplace(string)
+    answer = reverse_in_place(string)
 
     # Assert
     expect(answer).must_equal "a"
@@ -115,7 +112,7 @@
     string = ""
 
     # Act
-    answer = reverse_inplace(string)
+    answer = reverse_in_place(string)
 
     # Assert
     expect(answer).must_equal ""
@@ -125,7 +122,7 @@
     string = "apple"
 
     # Act
-    answer = reverse_inplace(string)
+    answer = reverse_in_place(string)
 
     # Assert
     expect(answer).must_equal "elppa"
@@ -227,40 +224,40 @@
   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
     # Arrange
     item = "x"
     array = ["b", "c", "a"]
-  
+
     # Act
     answer = search(array, item)
-  
+
     # Assert
     expect(answer).must_equal false
-    end
-
-    it "will return true when finding something at the front of the array" do
-      # Arrange
-      item = "b"
-      array = ["b", "c", "a"]
-    
-      # Act
-      answer = search(array, item)
-    
-      # Assert
-      expect(answer).must_equal true
-    end      
+  end
+
+  it "will return true when finding something at the front of the array" do
+    # Arrange
+    item = "b"
+    array = ["b", "c", "a"]
+
+    # Act
+    answer = search(array, item)
+
+    # Assert
+    expect(answer).must_equal true
+  end
 end
 
 xdescribe "is_palindrome" do
@@ -334,7 +331,7 @@
     # Assert
     expect(answer).must_equal 3
   end
-  
+
   it "returns 1 for (0, 0)" do
     # Arrange
     num1 = 0
@@ -346,7 +343,7 @@
     # Assert
     expect(answer).must_equal 1
   end
-  
+
   it "returns 1 for (10, 20)" do
     # Arrange
     num1 = 10