题解 | #DNA序列#

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String str = in.nextLine();
        int len = in.nextInt();
        in.close();

        double max = 0.0;
        String res = "";

        for(int i = 0; i <= str.length() - len; i++){
            String sub = str.substring(i,i + len);
            int c_len = len - sub.replaceAll("C","").length();
            int g_len = len - sub.replaceAll("G","").length();
            double num = ((double)(c_len + g_len)) / len;
            if(num > max){
                res = sub;
                max = num;
            }
        }

        System.out.println(res);
    }
}