sorting - I don't understand stable algorithm definition -


in computer science, stable sorting algorithm preserves order of records equal keys.

i don't understand why sorting algorithm stable , others none. basic sorting algorithm orders items of array of int. if create class or struct , use same algorithm considering swapping of whole object, , choosing order key, o age ecc, every algorithm can preserve order of records!

i think missed definition.

thanks lot.

say have array following:

a = [5, 4, 2a, 2b, 1]

where a , b there denote first 2 (2a) comes before second 2 (2b). in stable sorting algorithm, result be:

a_stable = [1, 2a, 2b, 4, 5]

that is, relative order of elements hasn't changed - 2a came before 2b in original array, , remains way in sorted array.

with non-stable algorithm, result be:

a_nonstable = [1, 2b, 2a, 4, 5]

this still correctly sorted, it's positions relative in original, unsorted array have changed.


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