如何删除字符串中给定区域中的重复字符？(假设我们有从中读取字符串的缓冲区)

public class RemoveDuplicates {
    public static void main(String[] args) {
        String buffer = "aabbccddeeffgg";
        int start = 2;
        int end = 8;
        
        String result = removeDuplicates(buffer, start, end);
        System.out.println(result);
    }
    
    public static String removeDuplicates(String buffer, int start, int end) {
        StringBuilder sb = new StringBuilder(buffer);
        HashSet<Character> set = new HashSet<>();
        
        for (int i = start; i <= end; i++) {
            char c = sb.charAt(i);
            
            if (set.contains(c)) {
                sb.deleteCharAt(i);
                end--;
                i--;
            } else {
                set.add(c);
            }
        }
        
        return sb.toString();
    }
}