3. 无重复字符的最长子串 - 力扣（LeetCode） (opens new window)

class Solution {
    public int lengthOfLongestSubstring(String s) {
        Map<Character, Integer> window = new HashMap<>();
        int left = 0, right = 0;
        int res = 0;
        while (right < s.length()) {
            char c = s.charAt(right);
            right++;
            // 进行窗口内数据的一系列更新
            window.put(c, window.getOrDefault(c,0) + 1);
            // 判断左侧窗口是否要收缩
            while (window.get(c) > 1) {
                char d = s.charAt(left);
                left++;
                // 进行窗口内数据的一系列更新
                window.put(d, window.getOrDefault(d,0) - 1);
            }
            // 在这里更新答案
            res = Math.max(res, right -left);
        }
        return res;
    }
}

**拼多多：**最多允许一对相邻重复字符的最长子串问题

public class Solution {
    public int longestSubstring(String s) {
        if (s == null || s.length() == 0) return 0;
        int left = 0, maxLen = 1, repeatCount = 0;
        
        for (int right = 1; right < s.length(); right++) {
            // 检查当前字符与前一个是否重复
            if (s.charAt(right) == s.charAt(right - 1)) {
                repeatCount++;
            }
            
            // 若相邻重复次数超过1，移动左指针直到合法
            while (repeatCount > 1) {
                if (s.charAt(left) == s.charAt(left + 1)) {
                    repeatCount--;
                }
                left++;
            }
            
            // 更新最大长度
            maxLen = Math.max(maxLen, right - left + 1);
        }
        return maxLen;
    }
}