Help optimize D solution to phone encoding problem: extremely slow performace.

[Jordan Wilson]

On Saturday, 13 January 2024 at 11:03:42 UTC, Renato wrote:
> I like to use a phone encoding problem to determine the 
> strenghtness and weaknesses of programming languages because 
> this problem is easy enough I can write solutions in any 
> language in a few hours, but complex enough to exercise lots of 
> interesting parts of the language.
>
> [...]

Hello Renato,

This seems to be quite a lot of calls:
```
======== Timer frequency unknown, Times are in Megaticks ========

   Num          Tree        Func        Per
   Calls        Time        Time        Call

19204964        3761        3756           0     pure nothrow ref 
@trusted immutable(char)[][] 
core.internal.array.appending._d_arrayappendcTX!(immutable(char)[][], immutable(char)[])._d_arrayappendcTX(scope return ref immutable(char)[][], ulong)

19204924        8957        3474           0     @safe void 
dencoder.printTranslations(immutable(char)[][][dencoder.Key], 
dencoder.ISolutionHandler, immutable(char)[], immutable(char)[], 
immutable(char)[][])
```

This is when using the `words-quarter.txt` input (the 
`dictionary.txt` input seems to finish much faster, although 
still slower than `java`/`rust`).

I also used only 100 phone numbers as input.

My final observation is that `words-quarter.txt` contains some 
1-letter inputs, (for example, `i` or `m`)...this may result in a 
large number of encoding permutations, which may explain the high 
number of recursion calls?

Jordan