Sockets - Erica

lib/recursive-methods.rb

@@ -1,49 +1,105 @@
 # Authoring recursive algorithms. Add comments including time and space complexity for each method.
 
-# Time complexity: ?
-# Space complexity: ?
+# NOTE: I tried my best with time and space complexity, but it just feels so strange with recursive methods.  Do you have any recommended resources
+# discussion time/space complexity, specifically with recursive methods?
+
+# Time complexity: O(n), where n is the number being passed in
+# Space complexity: O(n), where n is the number being passed in.  The method returns n * method(n-1).
+# So for 4, it would have to store:  4 * method(3), 3 * method(2), 2 * method(1), 1 * method(0) * 0.
 def factorial(n)
-    raise NotImplementedError, "Method not implemented"
+  raise ArgumentError if n < 0
+
+  if n == 0
+    return 1
+  else
+    return n * (factorial(n - 1))
+  end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2), where n is the length of the string
+# Space complexity: I'm not sure what the space complexity is.  I know that it is at least linear for the stack.  I am guessing that it might be O(n^2)
+# take into account that we are creating a new string each time
 def reverse(s)
-    raise NotImplementedError, "Method not implemented"
+  if s == ""
+    return ""
+  else
+    return s[-1] + reverse(s[0..-2])
+  end
 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.
+# Space complexity: O(n), where n is the length of the string. No extra space on top of the stack as the string is being changed in place
+def reverse_inplace(s, high_index: nil, low_index: nil)
+  high_index ||= s.length - 1
+  low_index ||= 0
+  return s if high_index <= low_index
+
+  s[high_index], s[low_index] = s[low_index], s[high_index]
+  high_index -= 1
+  low_index += 1
+  return reverse_inplace(s, high_index: high_index, low_index: low_index)
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n), where n is the size of the number
+# Space complexity: O(n), where n is the size of the number
 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), where n is the size of the string.
+# Space complexity: O(n^2), where n is the size of the string. Similarly to reverse(s) I think
 def nested(s)
-    raise NotImplementedError, "Method not implemented"
+  if s == ""
+    return true
+  elsif s[0] == "(" && s[-1] == ")"
+    return nested(s[1..-2])
+  else
+    return false
+  end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n^2), where n is the size of the string.
+# Space complexity: O(n^2), where n is the size of the string. Similarly to reverse(s) I think
 def search(array, value)
-    raise NotImplementedError, "Method not implemented"
+  if array.length == 0
+    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), where n is the size of the string.
+# Space complexity: O(n^2), where n is the size of the string.
 def is_palindrome(s)
-    raise NotImplementedError, "Method not implemented"
+  if s.length == 1 || s.length == 0
+    return true
+  elsif s[0] == s[-1]
+    return is_palindrome(s[1..-2])
+  else
+    return false
+  end
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(log[10] n), where n is proportional to the size of the number and smaller than m
+# Space complexity: O(log[10] n), where n is proportional to the size of the number and smaller than m
 def digit_match(n, m)
-    raise NotImplementedError, "Method not implemented"
-end
+  if n / 10 == 0 || m / 10 == 0
+    if n % 10 == m % 10
+      return 1
+    else
+      return 0
+    end
+  end
+
+  if n % 10 == m % 10
+    return 1 + digit_match(n / 10, m / 10)
+  else
+    return 0 + digit_match(n / 10, m / 10)
+  end
+end

specs/recursion_writing_spec.rb

@@ -1,7 +1,7 @@
-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"
 
 describe "factorial" do
   it "will find the factorial of 0" do
@@ -23,8 +23,7 @@
     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
@@ -38,7 +37,7 @@
   end
 end
 
-xdescribe "reverse" do
+describe "reverse" do
   it "will reverse 'cat'" do
     # Arrange
     string = "cat"
@@ -83,8 +82,7 @@
   end
 end
 
-
-xdescribe "reverse_in_place" do
+describe "reverse_in_place" do
   it "will reverse 'cat'" do
     # Arrange
     string = "cat"
@@ -129,7 +127,7 @@
   end
 end
 
-xdescribe "bunny" do
+describe "bunny" do
   it "returns 0 for 0 bunnies" do
     # Arrange
     count = 0
@@ -164,7 +162,7 @@
   end
 end
 
-xdescribe "nested" do
+describe "nested" do
   it "will return true for empystring" do
     # Arrange
     string = ""
@@ -210,7 +208,7 @@
   end
 end
 
-xdescribe "search" do
+describe "search" do
   it "will return false for empty array" do
     # Arrange
     item = "a"
@@ -224,43 +222,43 @@
   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
+describe "is_palindrome" do
   it "will return true for emptystring" do
     # Arrange
     string = ""
@@ -295,7 +293,7 @@
   end
 end
 
-xdescribe "digit_match" do
+describe "digit_match" do
   it "returns 4 for 1072503891 and 62530841" do
     # Arrange
     num1 = 1072503891
@@ -304,8 +302,8 @@
     # Act
     answer = digit_match(num1, num2)
 
-     # Assert
-     expect(answer).must_equal 4
+    # Assert
+    expect(answer).must_equal 4
   end
 
   it "returns 0 for nonmatching numbers" do
@@ -316,8 +314,8 @@
     # Act
     answer = digit_match(num1, num2)
 
-     # Assert
-     expect(answer).must_equal 0
+    # Assert
+    expect(answer).must_equal 0
   end
 
   it "returns 3 for 841 and 62530841" do
@@ -328,7 +326,7 @@
     # Act
     answer = digit_match(num1, num2)
 
-     # Assert
-     expect(answer).must_equal 3
+    # Assert
+    expect(answer).must_equal 3
   end
-end
+end