As with quicksort, quickselect is generally implemented as
an in-place algorithm, and beyond selecting the kth
element, it also partially sorts the data.
When the above is applicable, those quickselect implementations would violate the original assertion of:
Only the median (or pair around the median) needs to be
sorted, the other numbers can be unsorted
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From the Wikipedia page cited:
When the above is applicable, those quickselect implementations would violate the original assertion of: When the collection involved is immutable.