滑动窗口思路分析

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        int left = -1;
        int ans = 0;
        if(s.isEmpty()) return 0;
        if(n == 1) return 1;

        HashMap<Character, Integer> map = new HashMap<>();
        int firstIndex = 0;
        for (int i = 0; i < n; i++) {
            if(map.containsKey(s.charAt(i))){//保证数据的唯一性
                int index = map.get(s.charAt(i));
                int temp = index;
                while(index >= firstIndex && map.containsValue(index)){
                    map.remove(s.charAt(index--));
                }
                firstIndex = temp;
            }
            map.put(s.charAt(i), i);
            ans = Math.max(ans, map.size());
        }
        return ans;
    }
}

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        int left = -1;
        int ans = 0;
        HashSet<Character> set = new HashSet<>();//Set集合保证数据的唯一性
        for (int i = 0; i < n; i++) {
            if (i != 0){
                set.remove(s.charAt(i - 1));
            }
            while (left + 1 < n && !set.contains(s.charAt(left + 1))){
                set.add(s.charAt(left + 1));
                left++;
            }
            ans = Math.max(ans, left - i + 1);
        }
         return ans;
    }
}