题解 | #字符串出现次数的TopK问题#

TreeMap可以用于排序，通过自定义比较器对TreeMap进行排序

import java.util.*;


public class Solution {
    /**
     * return topK string
     * @param strings string字符串一维数组 strings
     * @param k int整型 the k
     * @return string字符串二维数组
     */
    public String[][] topKstrings (String[] strings, int k) {
        Map<String, Integer> map = new TreeMap<>();
        for (String str : strings) {
            map.put(str, map.getOrDefault(str, 0) + 1);
        }

        List<Map.Entry<String, Integer>> entryList = new ArrayList<>(map.entrySet());
        Collections.sort(entryList, new Comparator<Map.Entry<String, Integer>>() {
            @Override
            public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
                if (o1.getValue().equals(o2.getValue())) {
                    return o1.getKey().compareTo(o2.getKey());
                } else {
                    return o2.getValue().compareTo(o1.getValue());
                }
            }
        });
        String[][] ans = new String[k][2];
        int i = 0;
        for (Map.Entry<String, Integer> entry : entryList) {
            if (i < k) {
                ans[i][0] = entry.getKey();
                ans[i][1] = entry.getValue().toString();
                i++;
            }
        }
        return ans;
    }
}