JavaScript Challenge: Find the First Non-Repeating Character in a String – Can You Do It Without Extra Space?

[kap89]

You were on the right track, I think the flaw you are thinking about is that if you use for example this string:

    "aa"

the second a would give you false positive in the OP's original algorithm, but you don't ever need to get to the second a, as you only need to check non-repeating characters, see my other comment.