• 451. Sort Characters By Frequency


    Given a string, sort it in decreasing order based on the frequency of characters.

    Example 1:

    Input:
    "tree"
    
    Output:
    "eert"
    
    Explanation:
    'e' appears twice while 'r' and 't' both appear once.
    So 'e' must appear before both 'r' and 't'. Therefore "eetr" is also a valid answer.
    

    Example 2:

    Input:
    "cccaaa"
    
    Output:
    "cccaaa"
    
    Explanation:
    Both 'c' and 'a' appear three times, so "aaaccc" is also a valid answer.
    Note that "cacaca" is incorrect, as the same characters must be together.
    

    Example 3:

    Input:
    "Aabb"
    
    Output:
    "bbAa"
    
    Explanation:
    "bbaA" is also a valid answer, but "Aabb" is incorrect.
    Note that 'A' and 'a' are treated as two different characters.


    HashMap sort in Map.Entry<>
    public class Solution {
        public String frequencySort(String s) {
            HashMap<Character, Integer> map = new HashMap<>();
            for(int i = 0; i < s.length(); i ++){
                map.put(s.charAt(i), map.getOrDefault(s.charAt(i), 0) + 1);
            }
            ArrayList<Map.Entry<Character, Integer>> set = new ArrayList<Map.Entry<Character, Integer>>(map.entrySet());
            Collections.sort(set, new Comparator<Map.Entry<Character, Integer>>(){
                 public int compare(Map.Entry<Character, Integer> v1, Map.Entry<Character, Integer> v2){
                     return v2.getValue()-v1.getValue();
                 }
                });
            StringBuilder sb = new StringBuilder();
            for(Map.Entry<Character, Integer> k : set){
                int v = k.getValue();
                for(int i = 0 ; i < v ; i++){
                    sb.append(k.getKey().toString());
                }
            }
            return sb.toString();
        }
    }
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  • 原文地址:https://www.cnblogs.com/joannacode/p/6103492.html
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