Intersection of two sets

[Per Nordlöw]

On Tuesday, 3 December 2019 at 13:43:26 UTC, Jan Hönig wrote:
> pseudocode:
> alias set = bool[<something>]
> set foo = ...
> set bar = ...
> set result;

One simple optimization is to

set* smallest;
set* largest;

if (foo.length < bar.length)
{
     smallest = &foo;
     largest = &bar;
}
else
{
     smallest = &bar;
     largest = &foo;
}

> foreach(key; *smallest)
> {
>   if (key in *largest)
>   {
>     result[key] = true;
>   }
> }
> return result;

Provided that your set type has an `in`-operator with 
time-complexity O(1), this will, in the worst case, reduce time 
complexity from

     O(max(foo.length, bar.length))

to

     O(min(foo.length, bar.length))