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.next();
            int len = in.nextInt();
            String result = "";
            double max = 0.0;
            for (int i=0;i<= str.length() - len;i++){
                String sub = str.substring(i,i+len);
                double count = getCGRatio(sub);
                if (count > max){
                    max = count;
                    result = sub;
                }
            }
            System.out.println(result);
        }
    }

    static double getCGRatio(String str){
        int i = 0;
        for(Character c : str.toCharArray()){
            if (c =='C' || c == 'G'){
                i++;
            }
        }

        return (i + 0.0 ) / str.length();
    }
}