def length_of_longest_substring(s)
    longest = ""
    for i in 0..s.length
        for j in i..s.length
            brk = false
            s[i, j-i].each_char.with_index do |c, x|
                s[i, j-i].each_char.with_index do |c2, x2|
                    brk = true if c == c2 && x != x2
                end
                break if brk
            end
            longest = s[i, j-i] if (s[i, j-i].length > longest.length && !brk)
        end
    end
    return longest.length
end