力扣3-无重复字符的最长子串

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int res = 0;
        for(int i = 0; i < s.length(); i++) {
            Set<Character> set = new HashSet<>();
            for(int j = i; j < s.length(); j++) {
                if(set.contains(s.charAt(j))) break;
                res = Math.max(res, j - i + 1);
                set.add(s.charAt(j));
            }
        }
        return res;
    }
}

class Solution {
    public int lengthOfLongestSubstring(String s) {
        Set<Character> set = new HashSet<>();
        int right = -1, ans = 0;
        for(int i = 0; i < s.length(); i++) {
            if(i != 0) set.remove(s.charAt(i - 1));
            while(right + 1 < s.length() && !set.contains(s.charAt(right + 1))) {
                set.add(s.charAt(right + 1));
                ++right;
            }

            ans = Math.max(ans, right - i + 1);

        }

        return ans;
    }
}

class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s.equals("")) return 0;
        int start = 0, end = 0;
        int max = 1;
        HashSet<Character> set = new HashSet<>();
        while(end < s.length()) {
            char c_e = s.charAt(end);
            if(set.contains(c_e)) {
                set.remove(s.charAt(start));
                start++;
            } else {
                set.add(c_e);
                end++;
                max = Math.max(max, set.size());
            }
        }
        return max;
    }
}

    public int lengthOfLongestSubstring(String s) {
        int length = s.length();
        if (length < 2) return length;

        //双指针，将遇到的字符放进Map，看是不是重复的。
        Map<Character, Integer> map = new HashMap<>();
        char[] array = s.toCharArray();
        int size = 0;

        //窗口左指针
        int left = 0;

        for (int right = 0; right < length; right++) {
            //i是右指针
            if (map.containsKey(array[right])) {
                //如果包含了此元素，说明重复，需要移动左指针
                //窗口不能回退。
                left = Math.max(map.get(array[right]) + 1, left);
            }
            //修改当前元素索引
            map.put(array[right], right);
            //计算长度
            size = Math.max(size, right - left + 1);
        }
        return size;
    }