Swift-Longest Substring Without

Given a string, find the length of the longest substring without repeating characters.

Examples:

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", the answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

核心代码:

   func lengthOfLongestSubstring(_ s: String) -> Int {
        
        guard s.characters.count != 0 else {
            return 0
        }
        
        var set = Set<Character>()
        
        var chars = [Character](s.characters)
        var maxlen = 0
        var startIndex = 0
        
        for i in 0..<chars.count {
            
            let 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
    }