sorting - If the median of medians algorithm doesn't change the avg-case complexity of quicksort, why use it? -


given hard lower bound on sorting algorithm's average case complexity omega(n*lg(n)), when/why decide spend time implementing selection algorithm quicksort rather using random pivot or simple (n/2)th position in array?

because has better worst-case time complexity.

the approximate median-selection algorithm can used pivot strategy in quicksort, yielding optimal algorithm, worst-case complexity o(n log n). although approach optimizes quite well, typically outperformed in practice instead choosing random pivots, has average linear time selection , average log-linear time sorting, , avoids overhead of computing pivot. median of medians used in hybrid introselect algorithm fallback, ensure worst-case linear performance: introselect starts quickselect, obtain average performance, , falls median of medians if progress slow.


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