题解 | #DNA序列#，还是这种字符串的题有意思

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);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) { // 注意 while 处理多个 case
            String next = in.next();
            int i = in.nextInt();
            LinkedHashMap<Integer, Double> map = new LinkedHashMap<>();
            for (int j = 0,k = i; k < next.length(); j++,k++) {
                String s = next.substring(j, k);
                char[] chars = s.toCharArray();
                double count = 0;
                for (int z = 0; z < chars.length; z++) {
                    char c = chars[z];
                    if (c == 'G' || c == 'C'){
                        count++;
                    }
                }
                map.put(j,count/i);
            }

            Set<Map.Entry<Integer, Double>> entries = map.entrySet();
            int index = getIndex(entries);
            System.out.println(next.substring(index,index + i));
        }
    }

    public static int getIndex(Set<Map.Entry<Integer, Double>> entries){
        double max = 0;
        int index = 0;
        for (Map.Entry<Integer, Double> entry : entries) {
            Double value = entry.getValue();
            double v = Math.max(max, value);
            if (v != max){
                max = v;
                index = entry.getKey();
            }
        }
        return index;
    }
}