Branches -- Paige D. by minipaige02 · Pull Request #22 · Ada-C12/recursion-writing

minipaige02 · 2019-11-12T03:09:44Z

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CheezItMan

Overall nice work, you hit the learning goals here. Well done. Check my comments below especially with regard to time/space complexity. Let me know if you have questions.

CheezItMan · 2019-11-14T02:53:35Z

lib/recursive-methods.rb

-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def factorial(n)


CheezItMan · 2019-11-14T02:53:45Z

lib/recursive-methods.rb

 def reverse(s)
-    raise NotImplementedError, "Method not implemented"
+  return s if s.length <= 1
+  return s[-1] + reverse(s[1..-2]) + s[0]


s[1..-1] creates a new array and copies all the individual elements over and so is O(n) by itself.

CheezItMan · 2019-11-14T03:00:12Z

lib/recursive-methods.rb

-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def reverse(s)


This works, but the time/space complexities are actually O(n²) because you are generating a new array with each recursive call.

CheezItMan · 2019-11-14T03:00:24Z

lib/recursive-methods.rb

-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n)
+# Space complexity: O(n)
+def reverse_inplace(s, i = 0, j = s.length - 1)


CheezItMan · 2019-11-14T03:00:29Z

lib/recursive-methods.rb

-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def bunny(n)


CheezItMan · 2019-11-14T03:00:48Z

lib/recursive-methods.rb

-# Space complexity: ?
+# Time complexity: O(n)
+# Space complexity: O(n)
 def nested(s)


👍 This works, but you have similar time/space issues with the above methods.

CheezItMan · 2019-11-14T03:01:01Z

lib/recursive-methods.rb

-    raise NotImplementedError, "Method not implemented"
+# Time complexity: o(n)
+# Space complexity: O(n)
+def search(array, value, i = 0)


CheezItMan · 2019-11-14T03:01:16Z

lib/recursive-methods.rb

-    raise NotImplementedError, "Method not implemented"
+# Time complexity: O(n)
+# Space complexity: O(n)
+def is_palindrome(s, start_index = 0, last_index = s.length - 1)


CheezItMan · 2019-11-14T03:01:38Z

lib/recursive-methods.rb

-end
+# Time complexity: O(n) - where n is the number with less digits
+# Space complexity: O(n) - where n is the number with less digits
+def digit_match(n, m, match_count = 0)


minipaige02 · 2019-11-14T03:12:01Z

Thanks for your feedback, Chris! I can see now how some of my methods are creating new arrays each time and therefore greatly increasing the space complexity!

Added methods for each recursive method

c1a32bd

CheezItMan reviewed Nov 14, 2019

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Branches -- Paige D.#22

Branches -- Paige D.#22
minipaige02 wants to merge 1 commit intoAda-C12:masterfrom
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minipaige02 commented Nov 12, 2019

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minipaige02 commented Nov 14, 2019

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