Same thing in my solution where I downcased twice, not necessary. Only had to be done once.

Iterate once. Keep track of x's and o's. Compare their length at the end.

n < 2n

so, could you show us what is the solution if we have a long string?

for long strings it is strongly inefficient cause it's iterating over the array two times

Pretty cool. Didn't know there was a count method for strings.

you make me feel ashamed of my crazy coding.

This solution is not correct - try e.g. squareSum([2, 1, 2])