1081\. Smallest Subsequence of Distinct Characters

Medium

Given a string `s`, return _the lexicographically smallest subsequence of_ `s` _that contains all the distinct characters of_ `s` _exactly once_.

**Example 1:**

**Input:** s = "bcabc"

**Output:** "abc"

**Example 2:**

**Input:** s = "cbacdcbc"

**Output:** "acdb"

**Constraints:**

*   `1 <= s.length <= 1000`
*   `s` consists of lowercase English letters.

**Note:** This question is the same as 316: [https://leetcode.com/problems/remove-duplicate-letters/](https://leetcode.com/problems/remove-duplicate-letters/)