//至多包含两个不同字符的最长子串 长度
    func withMostTwoCharaters(original: String) -> Int {
        let array = Array(original)
        let count = array.count
        //1. 定义滑动窗口临时变量
        var map: [String: Int] = [:]
        var start = 0
        var maxLenght = 0
        
        //2. 遍历
        for end in 0..<count {
            // 更新临时变量
            let key = String(array[end])
            if let value = map[key] {
                map[key] = value + 1
            } else {
                map[key] = 1
            }
            var mapCount = map.count
            // 满足条件
            if mapCount <= 2 {
                maxLenght = max(maxLenght, end - start + 1)
            }
            //窗口不固定，用while,更新滑动窗口
            while mapCount > 2 {
                
                let key = String(array[start])
                if let value = map[key] {
                    if value - 1 == 0 {
                        map[key] = nil
                        mapCount -= 1
                    } else {
                        map[key] = value - 1
                    }
                }
                start += 1
            }
        }
        
        return maxLenght
    }