至少包含两个字符的最长字串

至少包含两个字符的最长字串

寻找字符串的最长子串，该子串最多只能存在两个不同的字符

示例 Input ：s= “aabbccc”

Output： “bbccc”；

滑动窗口+哈希表

public class Main {
    public static String findLongestSubstring(String s) {
        if (s == null || s.length() == 0) {
            return "";
        }

        int left = 0, right = 0;
        int maxLength = 0;
        int start = 0;
        Map<Character, Integer> charFrequency = new HashMap<>();

        while (right < s.length()) {
            char rightChar = s.charAt(right);
            charFrequency.put(rightChar, charFrequency.getOrDefault(rightChar, 0) + 1);
            right++;

            while (charFrequency.size() > 2) {
                char leftChar = s.charAt(left);
                charFrequency.put(leftChar, charFrequency.get(leftChar) - 1);
                if (charFrequency.get(leftChar) == 0) {
                    charFrequency.remove(leftChar);
                }
                left++;
            }
            if (right - left > maxLength) {
                maxLength = right - left;
                start = left;
            }
        }

        return s.substring(start, start + maxLength);
    }

    public static void main(String[] args) {
        String s = "aabbccc";
        System.out.println(findLongestSubstring(s));  // Output: "bbccc"
    }
}