Untitled

import java.util.*;

public class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        int n = s.length();
        if (n <= 10) return new ArrayList<>();

        Set<String> seen = new HashSet<>();
        Set<String> repeated = new HashSet<>();

        // Initialize StringBuilder with the first 10 characters
        StringBuilder currentWindow = new StringBuilder(s.substring(0, 10));

        // Add the initial substring to the seen set
        seen.add(currentWindow.toString());

        for (int i = 10; i < n; i++) {
            // Slide the window by removing the first character and adding the next character
            currentWindow.deleteCharAt(0);
            currentWindow.append(s.charAt(i));

            // Convert the current window to a string and check for repetition
            String windowString = currentWindow.toString();
            if (!seen.add(windowString)) {
                repeated.add(windowString);
            }
        }

        return new ArrayList<>(repeated);
    }
}