自定义Map.Entry的Comperator实现字符频率降序排序

 

 

leetCode （#451，middle） java实现

class Solution {
    public String frequencySort(String s) {
        Map<Character,Integer> map = new HashMap<>();
        
        //放入map
        for(char c :s.toCharArray()){
            if(map.containsKey(c)){
                map.put(c,map.get(c)+1);
            }else
                map.put(c,1);
        }
        //根据value的大小排序
        Comparator<Map.Entry<Character,Integer>> comparator =
            new Comparator<Map.Entry<Character, Integer>>() {
             @Override
             public int compare(Map.Entry<Character, Integer> o1, Map.Entry<Character, Integer> o2) {
                 return o2.getValue() - o1.getValue();
             }
         };
        //放入链表
        List<Map.Entry<Character,Integer>> list = new ArrayList<>(map.entrySet());
        //根据实现的comp排序
        Collections.sort(list,comparator);
        //定义数组
        StringBuilder sb = new StringBuilder();
        for(Map.Entry<Character,Integer> entry : list){
            for(int i = 0 ; i < entry.getValue();i++){
                sb.append(entry.getKey());
            }
        }
        return sb.toString();
        
    }
}