The repeated access to string is cache friendly, so has a good chance to be stupid fast.
On the other hand, memory allocations are stripped to (what seems to be) a minimum.
The clever avoidance of count and no intermediate collection to store the counting is appealing to the audiance. :-)
Also, codewars community tend to favor 'less code' approach. :-))
That's my understanding, but would like to hear someone more experienced in Rust.

why is this so highly voted? it's iterating over every string 26 times, once for every character in the alphabet. can someone explain?