/**

* Question Link: https://leetcode.com/problems/longest-substring-without-repeating-characters/

* Primary idea: Use a set to hold characters and then iterate the string,

* update maxLen, set, startIdx encountering duplicates

*

* Note: Swift does not have a way to access a character in a string with O(1),

* thus we have to first transfer the string to a character array

* Time Complexity: O(n), Space Complexity: O(n)

*

*/

class LongestSubstringWithoutRepeatingCharacters {

func lengthOfLongestSubstring(s: String) -> Int {

guard s.characters.count != 0 else {

return 0

}

var set = Set<Character>()

var maxLen = 0

var startIndex = 0

var chars = [Character](s.characters)

for i in 0 ..< chars.count {

var current = chars[i]

if set.contains(current) {

maxLen = max(maxLen, i - startIndex)

while chars[startIndex] != current {

set.remove(chars[startIndex])

startIndex += 1

}

startIndex += 1

} else {

set.insert(current)

}

}

maxLen = max(maxLen, chars.count - startIndex)

return maxLen

}