Why is sorting a string O(n log n)?
Sorting the characters in a string is not necessarily O(n log n).
- O(n log n) is the optimal value for a comparison sort. It is also the complexity of many languages' default sort implementation. However it's certainly possible to do worse than this. The complexity of sorting the characters in a string depends on the specific algorithm you choose to solve this task.
- It's also possible to do better than O(n log n) in some cases by using a sorting algorithm which is not a comparison sort. For example, if you know that you have an ASCII string with a maximum of 127 distinct characters you could use a counting sort which is O(n). A counting sort would also be feasible for Unicode strings where all characters are in in the Basic Multilingual Plane.
