leetcode451. 根据字符出现频率排序(JAVA)(hashmap)

 

 

my solution:

class Solution {
    public String frequencySort(String s) {
        Map map=new HashMap<>();
        List ret=new ArrayList();
        int []value=new int[s.toCharArray().length];
        int i=0;
        
        for(Character c:s.toCharArray())
        {
            map.put(c,map.getOrDefault(c,0)+1);
        }
        
        for(Character c:map.keySet())
        {
            value[i]=map.get(c);
            i++;
        }
        
        Arrays.sort(value);
        int times=0;
        int len=value.length;
        char ch='0';
        
        for(i=len-1;i>=0;i--)
        {
            times=value[i];
            for(Character c:map.keySet())
            {
                if(map.get(c)==times)
                {
                    map.put(c,0);
                    ch=c;
                    break;
                }
            }
            
            for(int j=0;j

dashen solution

class Solution {
    public String frequencySort(String s) {
        Map map = new HashMap();
        for(char c : s.toCharArray()) {
            map.put(c,map.getOrDefault(c,0)+1);
        }
        
        //System.out.println(map.toString());
        List candidates = new ArrayList(map.keySet());
        Collections.sort(candidates, (w1, w2) ->  map.get(w1) - map.get(w2));
        //System.out.println(candidates);
        StringBuilder x = new StringBuilder();
        for(int i = candidates.size() - 1; i>=0; i--) {
            int count = map.get(candidates.get(i));
            while(count-->0)
                x.append(candidates.get(i));
        }
        return x.toString();
    }
}

note:

1. 根据特定的关键字排序数组：利用Collections.sort（）方法

Collections.sort(candidates, (w1, w2) ->  map.get(w1) - map.get(w2));//根据映射的value值将关键字排序

详细算法：

List candidates = new ArrayList(map.keySet());

Collections.sort(candidates, (w1, w2) ->  map.get(w1) - map.get(w2));

 

 2.创建一个可变的string类型：StringBuilder x = new StringBuilder();

3.StringBuilder增加新内容：x.append(candidates.get(i));

4.将stringbuilder转化成string: x.toString()