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Add median() function using Quickselect (#12676)

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* Add median() function using Quickselect

* Update quick_select.py

* Update quick_select.py

* Update quick_select.py

---------

Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>
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Isidro 2025-05-21 20:33:29 +02:00 committed by GitHub
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searches/quick_select.py
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@ -60,3 +60,25 @@ def quick_select(items: list, index: int):
# must be in larger
else:
return quick_select(larger, index - (m + count))
def median(items: list):
"""
One common application of Quickselect is finding the median, which is
the middle element (or average of the two middle elements) in a sorted dataset.
It works efficiently on unsorted lists by partially sorting the data without
fully sorting the entire list.
>>> median([3, 2, 2, 9, 9])
3
>>> median([2, 2, 9, 9, 9, 3])
6.0
"""
mid, rem = divmod(len(items), 2)
if rem != 0:
return quick_select(items=items, index=mid)
else:
low_mid = quick_select(items=items, index=mid - 1)
high_mid = quick_select(items=items, index=mid)
return (low_mid + high_mid) / 2