zoukankan      html  css  js  c++  java
  • 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.

    The logic is very similar to NO.347 and here we just use a map a count and according to the frequency to put it into the right bucket. Then we go through the bucket to get the most frequently character and append that to the final stringbuilder.

    public String frequencySort(String s) {
            
            HashMap<Character, Integer> map = new HashMap<>();
            for (char c : s.toCharArray()) {
                map.put(c, map.getOrDefault(c, 0) + 1);
            }
            ArrayList<Character>[] list = new ArrayList[s.length() + 1];
            for (char c : map.keySet()) {
                int frequency = map.get(c);
                
                if (list[frequency] == null) {
                    list[frequency] = new ArrayList<>();
                }
                list[frequency].add(c);
            }
            StringBuilder sb = new StringBuilder();
            for (int i = s.length(); i >= 0; i--) {
                if (list[i] != null) {
                    for (char c : list[i]) {
                        for (int j = 0 ; j < (int)map.get(c); j++) {
                            sb.append(c);
                        }
                        
                    }
                }
            }
            return sb.toString();
        }
    

      

    public String frequencySort(String s) {
            Map<Character, Integer> map = new HashMap<>();
            for (char c : s.toCharArray()) {
                if (map.containsKey(c)) {
                    map.put(c, map.get(c) + 1);
                } else {
                    map.put(c, 1);
                }
            }
            PriorityQueue<Map.Entry<Character, Integer>> pq = new PriorityQueue<>(
                new Comparator<Map.Entry<Character, Integer>>() {
                    @Override
                    public int compare(Map.Entry<Character, Integer> a, Map.Entry<Character, Integer> b) {
                        return b.getValue() - a.getValue();
                    }
                }
            );
            pq.addAll(map.entrySet());
            StringBuilder sb = new StringBuilder();
            while (!pq.isEmpty()) {
                Map.Entry e = pq.poll();
                for (int i = 0; i < (int)e.getValue(); i++) {
                    sb.append(e.getKey());
                }
            }
            return sb.toString();
        }
    

      

  • 相关阅读:
    @RequestParam,@PathParam,@PathVariable,@QueryParam注解的使用区别
    关于android studio 出现Error:Execution failed for task ':app:preDebugAndroidTestBuild'. 的解决办法
    opencv:轮廓匹配
    opencv:图像轮廓计算
    opencv:图像轮廓发现
    opencv:联通组件扫描
    opencv:自适应阈值
    opencv:全局阈值
    opencv:二值图像的概念
    opencv:边缘提取
  • 原文地址:https://www.cnblogs.com/apanda009/p/7580690.html
Copyright © 2011-2022 走看看