Interview Cake
A stable sorting algorithm ensures that items that are equal to each other aren't reordered during the sorting process.
For instance, suppose we're sorting an array of computer science majors by their grade point average.
[('Mia', 3.9), ('Andrey', 3.2), ('Yvette', 3.9), ('Theo', 3.5), ('Charlie', 2.7)]
A stable sort will put Mia before Yvette in the sorted array, since Mia is before Yvette in the input.
[('Charlie', 2.7), ('Andrey', 3.2), ('Theo', 3.5), ('Mia', 3.9), ('Yvette', 3.9)]
An unstable sort doesn't offer any guarantees about Mia appearing before Yvette. So it's output might look like this:
[('Charlie', 2.7), ('Andrey', 3.2), ('Theo', 3.5), ('Yvette', 3.9), ('Mia', 3.9)]
These sorting algorithms are usually stable:
- counting sort
- merge sort
- insertion sort
These sorting algorithms are usually not stable:
- quicksort
- heapsort
- selection sort
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