题解 | #字符串出现次数的TopK问题#

import java.util.*;


public class Solution {
    
    public class ComparaTuple implements Comparator<ArrayList<String>> {
        @Override
        public int compare(ArrayList<String> arr1, ArrayList<String> arr2) {
            if (Integer.valueOf(arr1.get(1)) < Integer.valueOf(arr2.get(1))) {
                return 1;
            }
            else if (Integer.valueOf(arr1.get(1)) > Integer.valueOf(arr2.get(1))) {
                return -1;
            }
            else {
                return comparaString(arr1.get(0), arr2.get(0));
            }
        }
        public int comparaString(String str1, String str2) {
            int len1 = str1.length();
            int len2 = str2.length();
            int p1 = 0;
            int p2 = 0;
            
            int rs = 0;
            
            while (p1 < len1 && p2 < len2) {
                if (str1.charAt(p1) < str2.charAt(p2)) {
                    return -1;
                }
                else if (str1.charAt(p1) > str2.charAt(p2)) {
                    return 1;
                }
                else {
                    p1++;
                    p2++;
                }
            }
            
            if (p1 == len1 && p2 == len2) {
                rs = 0;
            }
            else if (p1 == len1) {
                rs = -1;
            }
            else {
                rs = 1;
            }
            return rs;
        }
    }
    
    /**
     * 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) {
        // write code here
        
        HashMap<String, Integer> hashMap = new HashMap<>();
        int num;
        Queue<String> queue = new LinkedList<>();
        
        Arrays.sort(strings);
        for (String str : strings) {
            
            if (!queue.contains(str)) {
                queue.add(str);
            }
            
            num = hashMap.getOrDefault(str, 0);
            num++;
            hashMap.put(str, num);
        }
        
        ArrayList<ArrayList<String>> arrayList = new ArrayList<>();
        String tmpStr;
        while (!queue.isEmpty()) {
            tmpStr = queue.poll();
            num = hashMap.get(tmpStr);
            ArrayList<String> tmpArrayList = new ArrayList<>();
            tmpArrayList.add(tmpStr);
            tmpArrayList.add(String.valueOf(num));
            arrayList.add(tmpArrayList);
        }
        
        arrayList.sort(new ComparaTuple());
        
        if (arrayList.size() < k) {
            return null;
        }
        
        String[][] rs = new String[k][2];
        for (int i = 0; i < k; i++) {
            rs[i][0] = arrayList.get(i).get(0);
            rs[i][1] = arrayList.get(i).get(1);
        }
        return rs;
    }
}