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);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) {
            String str = in.nextLine();
            int n = in.nextInt();
            dnaSort(str, n);
        }
    }

    public static void dnaSort(String str, int n) {
        HashMap<String, Double> map = new HashMap<>();
        ArrayList<String> list = new ArrayList<>();
        int left = 0;
        int right = n;
        while (right <= str.toCharArray().length) {
            String substr = str.substring(left, right);
            double gcCount = getGCCount(substr);
            map.put(substr, gcCount);
            list.add(substr);
            left++;
            right++;
        }

        Set<String> set = map.keySet();
        String maxKey = "" ;
        double maxV = 0.0;
        for (String key : list) {
            Double aDouble = map.get(key);
            if (aDouble == maxV) continue;
            if (aDouble > maxV) {
                maxV = aDouble;
                maxKey = key;
            }
        }
        System.out.println(maxKey);
    }

    public static double getGCCount(String str) {
        int count = 0;
        for (int i = 0; i < str.toCharArray().length; i++) {
            if (str.charAt(i) == 'G' || str.charAt(i) == 'C') {
                count++;
            }
        }
        if (count == 0) {
            return 0;
        } else {
            double length = str.toCharArray().length;
            return count / length;
        }

    }

}