Merge pull request #19 from alberthu16/day25

Day 25: change of vowels in cycle

Author: Albert Hu

day25/README.md

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+question of the day: https://codefights.com/challenge/CA2ShAfLkb5D5JHCG
+
+Given a text, reverse its characters and shift all of the vowels in a cycle.
+
+The vowels are 'a', 'e', 'i', 'o', and 'u' and can be upper- and lowercase.
+
+Example
+
+For cycle = 1 and text = "potato", the output should be
+changeOfVowelsInCycle(cycle, text) = "ototap".
+
+Reversed, the text becomes "otatop". The vowels in the text are 'o', 'a' and 'o' (in this exact order). When shifted by one, they become 'o', 'o' and 'a', so the final answer is "ototap".
+
+## Ideas
+
+I needa do two things: 1) reverse the string, 2) do the cycly thingy with the vowels.
+The cycly thingy is the slightly tricky part. However, I can just think of the
+vowels as a kind of circularly linked list where I can forget about parts of the list
+when I'm done with them. I can use a queue to hold the vowels that are in the process
+of being swapped into a new position. And I'll pop from this queue as I go through
+the indices of vowels that I need to swap.
+
+part 1 is `O(n)` runtime, and requires `O(n)` space because I create a list using the 
+characters of the string before I do the reversal.
+
+part 2 is `O(n)` runtime as well because in the worst case, all the input characters
+are vowels.
+
+So overall `O(n)` runtime, `O(n)` space. Is there a better solution? Maybe.
+
+## Code
+
+[Python](./changeOfVowelsInCycle.py)
+
+## Follow up
+

day25/changeOfVowelsInCycle.py

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+VOWELS = set(['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'])
+
+def changeOfVowelsInCycle(cycle, text):
+    rearranged = list(text)[::-1]
+    vowelIndexes = [i for i, c in enumerate(rearranged) if c in VOWELS]
+   
+    numVowels = len(vowelIndexes) 
+    if numVowels > 1:
+        
+        i = 0
+
+        saved = [rearranged[vowelIndexes[j]] for j in xrange(cycle % numVowels)]
+        while i < numVowels:
+            vowelIndex = vowelIndexes[(i + cycle) % numVowels]
+            saved.append(rearranged[vowelIndex])
+            rearranged[vowelIndex] = saved.pop(0)
+
+            i += 1
+        
+    return "".join(rearranged)
+
+def testChangeOfVowelsInCycle():
+    assert changeOfVowelsInCycle(1, "potato") == "ototap"
+    assert changeOfVowelsInCycle(3, "this test is of potato") == "itetip fo sa tsot soht"
+    assert changeOfVowelsInCycle(45, "aa bb cc dd ee ff gg hh ii jj") == "jj ea hh gg ff ai dd cc bb ie"
+    assert changeOfVowelsInCycle(1, "abc") == "cba"
+    assert changeOfVowelsInCycle(350, "a true magic is a potato think") == "knaht otatip i sa cegum airt o"
+    assert changeOfVowelsInCycle(9, "CodeFights") == "sthgiFedoC"
+    assert changeOfVowelsInCycle(10, "Ojf lsnelI UFlsn Eeiuo nnky Ynak jhA") == "ahj konY yknn uieEU nslFI elOnsl fjA"
+    assert changeOfVowelsInCycle(28, "Once upon a time there lived three little foxes") == "sexif elttel eirht davol ureht Omet o nepi ecne"
+
+def main():
+    testChangeOfVowelsInCycle()
+
+if __name__ == "__main__":
+    main()
+