# 1647. 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。

```python
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
        
```


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