sort-characters-by-frequency

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451. Sort Characters By Frequency (Medium)

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

 

Example 1:

Input: s = "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: s = "cccaaa"
Output: "aaaccc"
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: s = "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.

 

Constraints:

• 1 <= s.length <= 5 * 105
• s consists of English letters and digits.

Related Topics

[Hash Table] [String] [Bucket Sort] [Counting] [Sorting] [Heap (Priority Queue)]

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2. First Unique Character in a String (Easy)