[抄题]:
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.
[暴力解法]:
时间分析:
空间分析:
[优化后]:
时间分析:
空间分析:
[奇葩输出条件]:
[奇葩corner case]:
[思维问题]:
不知道怎么存进pq
[英文数据结构或算法,为什么不用别的数据结构或算法]:
只放一个hashmap元素:要用map.entrySet() 用得不多
Map.Entry代表一个哈希表实体
[一句话思路]:
[输入量]:空: 正常情况:特大:特小:程序里处理到的特殊情况:异常情况(不合法不合理的输入):
[画图]:
[一刷]:
Map.Entry中的
e.getKey()是不是字母,也不是对象。不用命名,直接存就行了
[二刷]:
[三刷]:
[四刷]:
[五刷]:
[五分钟肉眼debug的结果]:
[总结]:
pq中存Map.Entry 代表一个哈希表实体
[复杂度]:Time complexity: O(n) Space complexity: O(n)
[算法思想:迭代/递归/分治/贪心]:
[关键模板化代码]:
pq类中有类,类中有方法
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(); } } );
[其他解法]:
[Follow Up]:
[LC给出的题目变变变]:
[代码风格] :
[是否头一次写此类driver funcion的代码] :
[潜台词] :
class Solution { public String frequencySort(String s) { //ini: res map String res = new String(); Map<Character, Integer> map = new HashMap<>(); //cc if (s == null || s.length() == 0) return res; //count char char[] chars = s.toCharArray(); for (char c : chars) { if (map.containsKey(c)) { map.put(c, map.get(c) + 1); } else map.put(c, 1); } //pq PriorityQueue<Map.Entry<Character, Integer>> pq = 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(); } } ); //append to answer pq.addAll(map.entrySet()); StringBuilder sb = new StringBuilder(); while (!pq.isEmpty()) { Map.Entry e = pq.poll(); //char ch = e.getKey(); for (int i = 0; i < (int)e.getValue(); i++) { sb.append(e.getKey()); } } //return new string return sb.toString(); } }