Recursion-writing Gessica Mohr

Gemfile.lock

@@ -0,0 +1,36 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ansi (1.5.0)
+    builder (3.2.4)
+    coderay (1.1.3)
+    method_source (1.0.0)
+    minitest (5.14.2)
+    minitest-reporters (1.4.2)
+      ansi
+      builder
+      minitest (>= 5.0)
+      ruby-progressbar
+    minitest-skip (0.0.3)
+      minitest (~> 5.0)
+    minitest-spec (0.0.2.1)
+      minitest (>= 3.0)
+    pry (0.13.1)
+      coderay (~> 1.1)
+      method_source (~> 1.0)
+    rake (13.0.1)
+    ruby-progressbar (1.10.1)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  minitest
+  minitest-reporters
+  minitest-skip
+  minitest-spec
+  pry
+  rake
+
+BUNDLED WITH
+   2.1.4

lib/recursive-methods.rb

@@ -1,49 +1,91 @@
 # Authoring recursive algorithms. Add comments including time and space complexity for each method.
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(n) it depends on the size of n to run
+# Space complexity: O(n) it creates a stack every time it calls the recursive method
 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: ?
+# Time complexity: O(n^2) - the slice method in the reverse method creates another array so that counts for O(n) and then the method runs n times depending on the size of array, O(n). Total of O(n^2).
+# Space complexity: O(n^2) - because we are creating a new array when using the slice method and it creates a stack to run the recursion method.
 def reverse(s)
-    raise NotImplementedError, "Method not implemented"
+    if s.length <= 1
+        return s
+    end
+
+    return s[-1] + reverse(s[1..-2]) + s[0]
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+
+# Time complexity: O(n) it depends on the size of s to run
+# Space complexity: O(n) it creates a stack every time if calls the recursive method
+def reverse_inplace(s, i = 0, j = s.length - 1)
+    return s if s.length == 0 || s.length == 1
+    return s if i >= j
+    temp = s[i]
+    s[i] = s[j]
+    s[j] = temp
+
+    return reverse_inplace(s, i + 1, j - 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
+
+# Time complexity: O(n) it depends on the size of n to run
+# Space complexity: O(n) it creates a stack every time if calls the recursive method
 def bunny(n)
-    raise NotImplementedError, "Method not implemented"
+    return 0 if n <= 0
+    return 2 + bunny(n - 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def nested(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n) it depends on the size of s to run
+# Space complexity: O(n) it creates a stack every time if calls the recursive method
+def nested(s, i = 0, j = s.length - 1)
+    return true if s.empty? || i > j && s[i] != s[j]
+    return false if s.length == 1 || s[i] == s[j]
+    return nested(s, i + 1, j - 1)
+
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def search(array, value)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n) it depends on the size of the array to run
+# Space complexity: O(n) it creates a stack every time if calls the recursive method
+def search(array, value, index = 0)
+    return false if index >= array.length
+    return true if array[index] == value
+    return search(array, value, index + 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
-def is_palindrome(s)
-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n) it depends on the size of s to run
+# Space complexity: O(n) it creates a stack every time if calls the recursive method
+def is_palindrome(s, i = 0, j = s.length - 1)
+    return true if s.empty? || i >= j
+    return false if s[i] != s[j]
+
+    return is_palindrome(s, i + 1, j - 1)
 end
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(log n)
+# Space complexity: O(log n)
 def digit_match(n, m)
-    raise NotImplementedError, "Method not implemented"
+
+    return 1 if n == 0 && m == 0
+    return 0 if n <= 1 || m <= 1
+
+    if n % 10 == m % 10
+        return 1 + digit_match(n / 10, m / 10)
+    else
+        return digit_match(n / 10, m / 10)
+    end
+end
+
+
+
+# Time complexity: O(2^n) it depends on the size of n to run
+# Space complexity: O(2^n) it creates a stack every time if calls the recursive method
+def fibonacci(n)
+    return 0 if n == 0
+    return 1 if n == 1
+    return fibonacci(n - 1) + fibonacci(n - 2)
 end

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
@@ -359,3 +359,30 @@
     expect(answer).must_equal 1
   end
 end
+
+describe "fib" do
+  it "returns 0 for fib(0)" do
+    n = 0
+    answer = fibonacci(n)
+    expect(answer).must_equal 0
+  end
+
+  it "returns 1 for fibonnaci(1)" do
+
+    n = 1
+    answer = fibonacci(n)
+    expect(answer).must_equal 1
+  end
+
+  it "returns 3 for fibonnaci(4)" do
+    n = 4
+    answer = fibonacci(n)
+    expect(answer).must_equal 3
+  end
+
+  it "returns 34 for (9)" do
+    n = 9
+    answer = fibonacci(n)
+    expect(answer).must_equal 34
+  end
+end