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Daniela - Leaves #42

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47 changes: 36 additions & 11 deletions lib/recursive-methods.rb
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Original file line number Diff line number Diff line change
@@ -1,21 +1,46 @@
# Authoring recursive algorithms. Add comments including time and space complexity for each method.

# Time complexity: ?
# Space complexity: ?
# Time complexity: O(n), because of the size of the stack (number of methods that is accumulated in the stack to run)
# Space complexity: O(n), because of the size of this stack
def factorial(n)
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@CheezItMan CheezItMan Nov 14, 2019

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👍

raise NotImplementedError, "Method not implemented"
#Base Case
return 1 if n == 0
raise ArgumentError if n < 0

#Recursive Case
return n * factorial(n-1)
end

# Time complexity: ?
# Space complexity: ?
def reverse(s)
raise NotImplementedError, "Method not implemented"
# Time complexity: O(n), it will iterate through all elements of string
# Space complexity: O(1), it will always use same number of variables (i, j, memo)
def reverse(s )
i = 0
j = s.length - 1

while i < j
memo = s[i]
s[i] = s[j]
s[j] = memo

i += 1
j -= 1
end
Comment on lines +20 to +27
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@CheezItMan CheezItMan Nov 14, 2019

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A while loop, this is supposed to be recursive method 🤔

return s
end

# Time complexity: ?
# Space complexity: ?
def reverse_inplace(s)
raise NotImplementedError, "Method not implemented"
# Time complexity: O(n) ~ n/2 as increasing and decreasing both pointer in same call
# Space complexity: O(n), n/2 recursive calls,
# because both pointers are moving each time the method is called
def reverse_inplace(s, i = 0, j = s.length - 1)
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@CheezItMan CheezItMan Nov 14, 2019

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👍 Great work!

#Base Case
return s if i >= j

#Recursive Case
memo = s[i]
s[i] = s[j]
s[j] = memo
return reverse_inplace(s, i + 1, j - 1)

end

# Time complexity: ?
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4 changes: 2 additions & 2 deletions test/recursion_writing_test.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,7 @@
end
end

xdescribe "reverse" do
describe "reverse" do
it "will reverse 'cat'" do
# Arrange
string = "cat"
Expand Down Expand Up @@ -84,7 +84,7 @@
end


xdescribe "reverse_in_place" do
describe "reverse_in_place" do
it "will reverse 'cat'" do
# Arrange
string = "cat"
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