题解 | #DNA序列#

import java.util.Scanner;

// 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 num = in.nextInt();
        double originalRatio = 0.0;
        int index = 0;
        for (int i = 0; i + num <= str.length(); i++) {
            String subString = str.substring(i, i+num);
            String modifieds = subString.replaceAll("[^CG]", "");
            double ratio = (double) modifieds.length() / (double) num;
            if (ratio >  originalRatio) index = i;
            originalRatio = Math.max(originalRatio, ratio);
        }
        System.out.println(str.substring(index, index+num));
    }
}