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Ports - Ngoc #30

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Ports - Ngoc #30

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e22a963
added factorial method
lebaongoc Apr 11, 2019
a39668a
added time and space complexities
lebaongoc Apr 11, 2019
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15 changes: 12 additions & 3 deletions lib/factorial.rb
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@@ -1,6 +1,15 @@
# Computes factorial of the input number and returns it
# Time complexity: ?
# Space complexity: ?
# Time complexity: O(n)
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@mmcknett mmcknett Apr 13, 2019

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When you provide time complexity, please explain in a few words what n means. For example, in this case, is n equal to the value of number? Or is it equal to the number of things stored in number (which would be 1)? Or might it have anything to do with the number of decimal digits needed to represent number? It's important to define n for every new problem, since the meaning can change from algorithm to algorithm.

# Space complexity: O(1)
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@mmcknett mmcknett Apr 13, 2019

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Also briefly explain why here.

def factorial(number)
raise NotImplementedError
if number == nil
raise ArgumentError
end

i = 1
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@mmcknett mmcknett Apr 13, 2019

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I'm used to seeing i used as a variable name only when the variable is used to iterate over a collection. This variable is actually being used to accumulate the product of numbers for the factorial calculation. I'd name this something more like product in order to avoid confusion.

while number > 0
i = number * i
number -= 1
end
return i
end