If you know there are only two states, why not have a bool that you flip each time?
is_even = !is_even should be a lot cheaper than string comparison or modulus, assuming a reasonable language.
is_even = !is_even should be a lot cheaper than string comparison or modulus, assuming a reasonable language.
My idea with that is that it's extremely important to reach that conclusion, as it matches the problem perfectly and thus is much more efficient than our (often natural) standard approach of mod(x,2).
When you've reached that step, you can further improve by using a boolean instead of a short string, but that steps clearly into optimization, as it's not "formulating the problem correctly" but "finding a better way to implement the same solution".
There is major cost in not formulating the problem correctly (even odd is an approach to alternating colors, not the problem itself), and mod for table rows is a prime example of that.