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Leaves - Morgan #40

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79 changes: 52 additions & 27 deletions lib/recursive-methods.rb
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Original file line number Diff line number Diff line change
@@ -1,49 +1,74 @@
# Authoring recursive algorithms. Add comments including time and space complexity for each method.

# Time complexity: ?
# Space complexity: ?
def factorial(n)
raise NotImplementedError, "Method not implemented"
# Time complexity: O(n) -- I think all of my methods might be this space/time complexity but not positive!
# Space complexity: O(n)
def factorial(num)
raise ArgumentError if num < 0
return num * factorial(num - 1)
end
Comment on lines +5 to 8
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@CheezItMan CheezItMan Nov 14, 2019

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You're missing a base case here.

def factorial(num)
  raise ArgumentError, "Cannot accept a number < 0"
  return 1 if num <= 1

  return num * factorial(num - 1)
end


# Time complexity: ?
# Space complexity: ?
# Time complexity: 0(n)
# Space complexity: O(n)
def reverse(s)
raise NotImplementedError, "Method not implemented"
if s.length > 1 then
((s[s.length - 1, 1] = s[(s.length - (s.length + 1)), 1]) + reverse_recursive(s.length - 1))
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@CheezItMan CheezItMan Nov 14, 2019

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You don't have a reverse_recursive method 🤔

else
s
end
end

# Time complexity: ?
# Space complexity: ?
# Time complexity: O(n)
# Space complexity: O(n)
def reverse_inplace(s)
raise NotImplementedError, "Method not implemented"
return s if s.length <= 1
reversed_str = reverse(s[1..-1])
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@CheezItMan CheezItMan Nov 14, 2019

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You're calling the reverse method in the method above here.

It's also in no way in place.

reversed_str += s[0]
reversed_str
end

# Time complexity: ?
# Space complexity: ?
# Time complexity: O(n)
# Space complexity: O(n)
def bunny(n)
raise NotImplementedError, "Method not implemented"
return 0 if n < 1
return 2 if n == 1
return 2 + bunny(n-1)
end

# Time complexity: ?
# Space complexity: ?
# Time complexity: O(n)
# Space complexity: O(n)
def nested(s)
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👍 This works, although since you are creating a new array with s[1..s.length-2] your time & space complexities are off.

They should be O(n2)

raise NotImplementedError, "Method not implemented"
return true if s.length == 0
if s[0] == "(" && s[-1] == ")"
return nested(s[1..s.length-2])
else
return false
end
end

# Time complexity: ?
# Space complexity: ?
def search(array, value)
raise NotImplementedError, "Method not implemented"
# Time complexity: O(n)
# Space complexity: O(n)
def search(array, value, index = 0)
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@CheezItMan CheezItMan Nov 14, 2019

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You're never calling this method with another index number, so you don't need this argument.

Alternatively you don't need to create a new array and instead call the method with an increasing index.

return false if array.empty?
return true if array[index] == value
return search(array[1..-1], value)
end

# Time complexity: ?
# Space complexity: ?
# Time complexity: O(n)
# Space complexity: O(n)
def is_palindrome(s)
raise NotImplementedError, "Method not implemented"
return true if s.empty? || s.length == 1
return false if s[0] != s[s.length -1]
return is_palindrome(s, 1)
end

# Time complexity: ?
# Space complexity: ?
# Time complexity: O(n)
# Space complexity: O(n)
def digit_match(n, m)
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👍

raise NotImplementedError, "Method not implemented"
n = n.to_s
m = m.to_s
return 0 if n[-1] == nil || m[-1] == nil
if n[-1] == m[-1]
return 1 + digit_match(n[0..-2], m[0..-2])
else
return digit_match(n[0..-2], m[0..-2])
end
end
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