India - Water

lib/recursive-methods.rb

@@ -1,27 +1,49 @@
 # 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
+        return 1
+    elsif n < 0
+        raise ArgumentError
+    else
+        return n * factorial(n-1)
+    end
 end
 
+puts factorial(5)
+
 # Time complexity: ?
 # Space complexity: ?
 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: ?
+# Time complexity: O(n^2)
+# Space complexity: O(n^2)
 def reverse_inplace(s)
-    raise NotImplementedError, "Method not implemented"
+    if s.length <=1
+        return s
+    end
+
+    new_s = reverse_inplace(s[1..-2])
+    s[1..-2] = new_s
+    s[0] , s[-1] = s[-1], s[0]
+    return s
 end
 
-# Time complexity: ?
-# Space complexity: ?
+puts reverse_inplace("hello world")
+
+# 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: ?
@@ -30,16 +52,28 @@ def nested(s)
     raise NotImplementedError, "Method not implemented"
 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[0] == value
+        return true
+    elsif array.length < 1
+        return false
+    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
+        return true
+    elsif s[0] != s[-1]
+        return false
+    else
+        return is_palindrome(s[1..-2])
+    end
 end
 
 # Time complexity: ?

test/recursion_writing_test.rb

@@ -213,7 +213,7 @@
   end
 end
 
-xdescribe "search" do
+describe "search" do
   it "will return false for empty array" do
     # Arrange
     item = "a"
@@ -242,10 +242,10 @@
     # Arrange
     item = "x"
     array = ["b", "c", "a"]
-  
+
     # Act
     answer = search(array, item)
-  
+
     # Assert
     expect(answer).must_equal false
     end
@@ -254,16 +254,16 @@
       # Arrange
       item = "b"
       array = ["b", "c", "a"]
-    
+
       # Act
       answer = search(array, item)
-    
+
       # Assert
       expect(answer).must_equal true
-    end      
+    end
 end
 
-xdescribe "is_palindrome" do
+describe "is_palindrome" do
   it "will return true for emptystring" do
     # Arrange
     string = ""
@@ -334,7 +334,7 @@
     # Assert
     expect(answer).must_equal 3
   end
-  
+
   it "returns 1 for (0, 0)" do
     # Arrange
     num1 = 0
@@ -346,7 +346,7 @@
     # Assert
     expect(answer).must_equal 1
   end
-  
+
   it "returns 1 for (10, 20)" do
     # Arrange
     num1 = 10