To generate 1_000_000 numbers

acc <> Integer.to_string(round(:rand.uniform))     # fastest   379.2ms
acc <> Integer.to_string(:rand.uniform(2) - 1)     # fast      533.9ms
"#{acc}#{Integer.to_string(round(:rand.uniform))}" # slow      1797.8ms
Integer.to_string(round(:rand.uniform)) <> acc     # slowest   37525.1ms

I tried with Integer.to_string(:rand.uniform(2) - 1) <> acc, and it timed out. Do you know why the order matters?

Need to pass the test... it was the precision causing the problem.

Like this solution!

|> (&(&1 -- ids)).()

can be replaced as

|> Kernel.--(ids)

Looks better this way :)