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);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) { // 注意 while 处理多个 case
            String str = in.nextLine();
            int n = in.nextInt();
            String ans = "";
            Double cg = -1.0;
            int left = 0; 
            int right = n - 1;
            while (right < str.length()) {
                String str1 = str.substring(left, right + 1);
                String str2 = str1.replaceAll("[^CG]", "");
                Double cg1 = str2.length() * 1.0 / str1.length();
                if (cg1 > cg) {
                    cg = cg1;
                    ans = str1;
                }
                left++;
                right++;
            }
            System.out.println(ans);
        }
    }
}