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Perfect square using binary search #2351

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Merged
cclauss merged 3 commits into from
Aug 25, 2020
Merged

Perfect square using binary search #2351

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022cc8e
Add perfect_square_binary_search
ihebu Aug 25, 2020
d95b208
Update tests
ihebu Aug 25, 2020
f2ccef9
Add tests
ihebu Aug 25, 2020
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46 changes: 46 additions & 0 deletions maths/perfect_square.py
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,52 @@ def perfect_square(num: int) -> bool:
return math.sqrt(num) * math.sqrt(num) == num


def perfect_square_binary_search(n: int) -> bool:
"""
Check if a number is perfect square using binary search.
Time complexity : O(Log(n))
Space complexity: O(1)

>>> perfect_square_binary_search(9)
True
>>> perfect_square_binary_search(16)
True
>>> perfect_square_binary_search(1)
True
>>> perfect_square_binary_search(0)
True
>>> perfect_square_binary_search(10)
False

@cclauss cclauss Aug 25, 2020

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tests for -1, 1.1, "a", None, []?

@ihebu ihebu Aug 25, 2020

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should I first add input validation inside the function, or should I just include those tests ?

@cclauss cclauss Aug 25, 2020 •
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Write the tests first and see how your function deals with unexpected input. The trick is to not write validation code if you don't have to. If your function is already going to raise an IndexError, TypeError, ValueError, etc. then you have no work to do. Just look for cases where your code would silently fail or would deliver nonsense results.

@ihebu ihebu Aug 25, 2020

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Got it.Thank you so much !
Things should be good now.

>>> perfect_square_binary_search(-1)
False
>>> perfect_square_binary_search(1.1)
False
>>> perfect_square_binary_search("a")
Traceback (most recent call last):
...
TypeError: '<=' not supported between instances of 'int' and 'str'
>>> perfect_square_binary_search(None)
Traceback (most recent call last):
...
TypeError: '<=' not supported between instances of 'int' and 'NoneType'
>>> perfect_square_binary_search([])
Traceback (most recent call last):
...
TypeError: '<=' not supported between instances of 'int' and 'list'
"""
left = 0
right = n
while left <= right:
mid = (left + right) // 2
if mid ** 2 == n:
return True
elif mid ** 2 > n:
right = mid - 1
else:
left = mid + 1
return False


if __name__ == "__main__":
import doctest

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