标签：dal example sem NPU pair note fir def top
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.
给定一个字符串，请将字符串里的字符按照出现的频率降序排列。
基本思路就是遍历一遍字符串，将字符出现的次数存进Hashmap中，再遍历一遍Hashmap将字符和出现次数作为一组pair存进优先级队列中，再从队列中依次取出数据拼接成最后的字符串。
C++
class Solution { public: string frequencySort(string s) { unordered_map<char, int> m; for(const auto& c:s) m[c]++; priority_queue <pair<char, int>, vector<pair<char, int>>, cmp >q; for(const auto& i:m){ q.push(make_pair(i.first, i.second)); } string res = ""; while(!q.empty()){ res.append(q.top().second, q.top().first); q.pop(); } return res; } private: struct cmp{ bool operator() (pair<char, int> a, pair<char, int> b) { return a.second < b.second; } }; };
Java
class Solution { public String frequencySort(String s) { for(char c:s.toCharArray()){ map.put(c, map.getOrDefault(c,0) + 1); } p.addAll(map.entrySet()); while(!p.isEmpty()){ Map.Entry<Character, Integer> e = p.poll(); for(int i = 0; i < e.getValue().intValue(); i++){ res.append(e.getKey()); } } return res.toString(); } private StringBuilder res = new StringBuilder(); private HashMap<Character, Integer> map = new HashMap<>(); private PriorityQueue<Map.Entry<Character, Integer>> p = new PriorityQueue<>(new Comparator<Map.Entry<Character, Integer>>() { public int compare(Map.Entry<Character, Integer> a, Map.Entry<Character, Integer> b) { return b.getValue() - a.getValue(); } }); }
LeetCode 451. Sort Characters By Frequency 根据字符出现频率排序 (C++/Java)
标签：dal example sem NPU pair note fir def top
原文地址：https://www.cnblogs.com/silentteller/p/12181672.html
