There are many ways to design a graph data structure. All of them
have tradeoffs, they can't be very good for everything.
For your benchmarks are you using the ldc2 compiler with correct
compilation switches?
map() should not allocate memory.
Sometimes lazy code is faster and sometimes it's slower. A good
compiler (like Haskell GHC) should be able to optimize map well.
Also try to use a bitvector from Phobos instead of bool[].
Sometimes you can keep memory allocation low, performance almost
acceptable, and code easy to read using a pre-allocated scratch
space plus using map() and copy() from std.algorithm.
Bye,
bearophile
