sort characters by frequency medium

String/SortCharactersByFrequency.py

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+"""
+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，以字符出现的频率进行排序。
+
+思路：
+1. 用一个字典记录每个字符出现的频率。
+2. 根据出现的频率排序。
+3. 因为直接堆在一起即可，直接构建一个列表。
+4. 在组合起来。
+
+beat 95% 36ms.
+
+测试地址:
+https://leetcode.com/problems/sort-characters-by-frequency/description/
+
+"""
+class Solution(object):
+    def frequencySort(self, s):
+        """
+        :type s: str
+        :rtype: str
+        """
+
+        x = {}
+
+        for i in s:
+            try:
+                x[i] += 1
+            except:
+                x[i] = 1
+
+        b = sorted(x, key=lambda t: x[t], reverse=True)
+
+        return ''.join([i*x[i] for i in b])
+