I have to say it is a ugly feature of ruby to use % for formatting. I would rather use sprintf or other helper methods to achieve this.

I think total is better, it stands for the sum of all previous results.

This is so clever. I didn't know String.prototype.replace's real power!

"Test Failed: Should parse numbers - Expected: 3, instead got: 3", WTF is this!?

I suggest you to add some trivial examples. That would help others solve this kata.

Thanks. I struggled with that for a while. After removing the \n at the last line, my solution got passed. Nice kata! I think it's 5kyu.

Also, it should be documented that whether the last line should contain \n or not.

The image is missing, pls fix that.

My code run through a test with 9999999 items within 0.5s, which is surely high efficient enough.

I used BST and it is still timeout. I did massive tests, none of them failed. Maybe you should adjust the time limit.