3.无重复字符的最长子串

https://leetcode-cn.com/problems/longest-substring-without-repeating-characters/

    /**
     *  法一： 滑动窗口
     */
    public int lengthOfLongestSubstring(String s) {
        if (s == null || s.length() == 0) {
            return 0;
        }
        char[] str = s.toCharArray();
        //记录遍历过的字符
        Set<Character> set = new HashSet<>();
        int len = Integer.MIN_VALUE;
        //滑动窗口
        int R = -1;
        for (int L = 0; L < s.length(); L++) {
            if (L != 0) {
                set.remove(str[L - 1]);
            }
            // R往右扩到不能再扩
            while (R + 1 < s.length() && !set.contains(str[R + 1])) {
           、、     set.add(str[++R]);
            }
            len = Math.max(len, R - L + 1);;
        }
        return len;
    }