`func lengthOfLongestSubstring(_ s: String) -> Int {
var maxCount = 0
var currentString = ""
for char in s {
if let containIndex = currentString.firstIndex(of: char) {
currentString.removeSubrange(currentString.startIndex...containIndex)
currentString.append(char)
}else{
currentString.append(char)
maxCount = max(maxCount, currentString.count)
}
}
\
return maxCount
}`
