力扣3. 无重复字符的最长子串

class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s.length()==0 || s==null) return 0;
        int left = 0;
        int right = 0;
        int max = 0;
        boolean[] used = new boolean[128];
        while(right < s.length()){
            if(used[s.charAt(right)] == false){
                used[s.charAt(right)] = true;
                right++;
            }
            else{
                max = Math.max(max, right-left);//必须要先判断一次：bcada
                if(left < right && s.charAt(left) != s.charAt(right)){
                    used[s.charAt(left)] = false;
                    left++;
                }
                else{
                    left++;
                    right++;
                }
            }
        }
        return max = Math.max(max, right-left);//Math.max也是必须要的，比如a
    }
}