Question

My friend was asked a question in his interview:

The interviewer gave him an array of unsorted numbers and asked him to sort. The restriction is that the number of writes should be minimized while there is no limitation on the number of reads.

Answer 1

If the array is shorter (ie less than about 100 elements) a Selection sort is often the best choice if you also want to reduce the number of writes.

From wikipedia:

Another key difference is that
selection sort always performs Θ(n)
swaps, while insertion sort performs
Θ(n²) swaps in the average and worst
cases. Because swaps require writing
to the array, selection sort is
preferable if writing to memory is
significantly more expensive than
reading. This is generally the case if
the items are huge but the keys are
small. Another example where writing
times are crucial is an array stored
in EEPROM or Flash. There is no other
algorithm with less data movement.

For larger arrays/lists Quicksort and friends will provide better performance, but may still likely need more writes than a selection sort.

If you’re interested this is a fantastic sort visualization site that allows you to watch specific sort algorithms do their job and also “race” different sort algorithms against each other.