func lengthOfLongestSubstring(s string) int {
    l:=0
    res:=0
    set:=map[byte]bool{}

    for r,_:= range s {
        _,f:=set[s[r]]
        for f {
            delete(set,s[l])
            l++
              _,f=set[s[r]]
        }
        set[s[r]] = true
        res = max(res,r - l + 1)
    }
    return res
}
func max(l,r int) int {
    if l > r {
        return l
    }
    return r
}