1647. Minimum Deletions to Make Character Frequencies Unique

https://leetcode.com/problems/minimum-deletions-to-make-character-frequencies-unique/

A string s is called good if there are no two different characters in s that have the same frequency.

Given a string s, return the minimum number of characters you need to delete to make s good.

The frequency of a character in a string is the number of times it appears in the string. For example, in the string "aab", the frequency of 'a' is 2, while the frequency of 'b' is 1.

Example 1:

Input: s = "aab"
Output: 0
Explanation: s is already good.

Example 2:

Input: s = "aaabbbcc"
Output: 2
Explanation: You can delete two 'b's resulting in the good string "aaabcc".
Another way it to delete one 'b' and one 'c' resulting in the good string "aaabbc".

Example 3:

Input: s = "ceabaacb"
Output: 2
Explanation: You can delete both 'c's resulting in the good string "eabaab".
Note that we only care about characters that are still in the string at the end (i.e. frequency of 0 is ignored).

Constraints:

• 1 <= s.length <= 10**5

• s contains only lowercase English letters.

由小写字母组成的字符串，问最少去掉多少字符能使得字符串中每个字符出现频次是唯一的。贪心地将每个字符出现的频次不断减一，直到是唯一频次。

class Solution:
    def minDeletions(self, s: str) -> int:
        cnt, used, res = collections.Counter(s), set(), 0
        for _, f in cnt.items():
            while f > 0 and f in used:
                res += 1
                f -= 1
            used.add(f)
        return res