Janice Lichtman - Recursion writing

README.md

@@ -6,6 +6,7 @@ Write a method `factorial` that accepts an integer parameter n and that uses rec
 
 - e.g. fact(4) = 4 * 3 * 2 * 1 = 24
 
+
 ### Write #2
 `reverse(s)`
 Write a method `reverse` that accepts a string as a parameter

recursive-methods.rb

@@ -1,16 +1,125 @@
 
 def factorial(n)
+  raise ArgumentError.new("Not an integer") if
+  !(n.class==Integer)
+  raise ArgumentError.new("Not a non-negative integer") if n < 0
+  if n==0
+    return 1
+  else
+    return n * factorial(n-1)
+  end
 end
 
+
+#with tail recursion (just for fun):
+def factorialB(n, total=1)
+  raise ArgumentError.new("Not an integer") if
+  !(n.class==Integer)
+  raise ArgumentError.new("Not a non-negative integer") if n < 0
+
+  if n==0
+    return total
+  else
+    return factorialB(n-1, n * total)
+  end
+end
+
+
 def reverse(s)
+  if s.nil? || s.length==0
+    return ""
+  else
+    return reverse(s[1..-1])+s[0]
+  end
 end
 
+
 def bunny(n)
+  raise ArgumentError.new("Not an integer") if
+  !(n.class==Integer)
+  raise ArgumentError.new("Not a non-negative integer") if n < 0
+  if n==0
+    return 0
+  else
+    return bunny(n-1) + 2
+  end
 end
 
-def nested(s)
+
+#Accepts ()() as acceptable 'nestings' of parentheses.
+def nested(s,  counter = 0)
+  s.each_char do |paren|
+    raise ArgumentError.new("Includes non-paren characters") if !['(',')'].include?(paren)
+  end
+
+  if s.length == 0
+    (counter == 0)? true:false
+  elsif s[0]=='('
+    counter += 1
+    return nested(s[1..-1], counter)
+  elsif s[0]==')'
+    counter -= 1
+    if counter < 0
+      return false
+    else
+      return nested(s[1..-1], counter)
+    end
+  end
+end
+
+
+# Only accepts strictly nested strings of parenteses.
+# Ex ()() will count as false.
+def strictly_nested(s,  counter = 0)
+  s.each_char do |paren|
+    raise ArgumentError.new("Includes non-paren characters") if !['(',')'].include?(paren)
+  end
+
+  if s.length == 0
+    (counter == 0)? true:false
+  elsif s[0]=='('
+    counter += 1
+    return strictly_nested(s[1..-1], counter)
+  elsif s[0]==')'
+    counter -= 1
+    #Since we only want strictly nested parentheses [ie don't want to allow ()() ], if counter hits 0 and there are more characters in the string, the method should return false.
+    if counter == 0 && s.length != 1
+      return false
+    else
+      return strictly_nested(s[1..-1], counter)
+    end
+  end
 end
 
+
+####### Added Fun
+
+def fib(n)
+  raise ArgumentError.new("Not an integer") if
+  !(n.class==Integer)
+  raise ArgumentError.new("Not a positive integer") if n < 0
+  if n == 1
+    return 1
+  elsif n == 2
+    return 1
+  else
+    return fib(n-1) + fib(n-2)
+  end
+end
+
+
+def pal(s)
+  if (s.length == 1) || (s.length == 0)
+    return true
+  elsif s[0] == s[-1]
+    return pal(s[1..-2])
+  else
+    return false
+  end
+end
+
+
+
 # Factorial Tests
 raise "factorial broke - factorial(4)" unless factorial(4) == 24
 raise "factorial broke - factorial(0)" unless factorial(0) == 1
@@ -26,9 +135,12 @@ def nested(s)
 raise "bunny broke - bunny(10)" unless bunny(10) == 20
 puts "passes all bunny tests"
 
-# Nested Tests
-raise "nested broke - nested('((()))')" unless reverse("((()))") == true
-raise "nested broke - nested('())')" unless reverse("())") == false
-puts "passes all nested tests"
+# # Nested Tests
+# raise "nested broke - nested('((()))')" unless reverse("((()))") == true
+# raise "nested broke - nested('())')" unless reverse("())") == false
+# puts "passes all nested tests"
+
+puts 'typo in the nested tests. written as reverse instead of nested'
+
 
 puts "All test passed"

sandbox.rb

@@ -0,0 +1,23 @@
+# Only accepts strictly nested strings of parenteses.
+# Ex ()() will count as false.
+
+def strictly_nested(s,  counter = 0)
+  s.each_char do |paren|
+    raise ArgumentError.new("Includes non-paren characters") if !['(',')'].include?(paren)
+  end
+
+  if s.length == 0
+    (counter == 0)? true:false
+  elsif s[0]=='('
+    counter += 1
+    return strictly_nested(s[1..-1], counter)
+  elsif s[0]==')'
+    counter -= 1
+    #Since we only want strictly nested parentheses [ie don't want to allow ()() ], if counter hits 0 and there are more characters in the string, the method should return false.
+    if counter == 0 && s.length != 1
+      return false
+    else
+      return strictly_nested(s[1..-1], counter)
+    end
+  end
+end