题解 | #DNA序列#

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            String line = sc.nextLine();
            int n = Integer.parseInt(sc.nextLine());
            if (line.length() == n) {
                System.out.println(line);
                return;
            }
            int max = Integer.MIN_VALUE;
            Map<String, Integer> map = new LinkedHashMap<>();
            for (int i = 0; i < line.length() - n + 1; i++) {
                String substring = line.substring(i, i + n);
                int count = 0;
                for (char c : substring.toCharArray()) {
                    if (c == 'C' || c == 'G') {
                        count++;
                    }
                }
                max = Math.max(max, count);
                map.put(substring, count);
            }
            for (Map.Entry<String, Integer> entry : map.entrySet()) {
                if (entry.getValue() == max) {
                    System.out.println(entry.getKey());
                    break;
                }
            }
        }
        sc.close();
    }
}