Return the lexicographically smallest subsequence of text that contains all the distinct characters of text exactly once.
Example 1:
Input: "cdadabcc" Output: "adbc"
Example 2:
Input: "abcd" Output: "abcd"
Example 3:
Input: "ecbacba" Output: "eacb"
Example 4:
Input: "leetcode" Output: "letcod"
Constraints:
1 <= text.length <= 1000textconsists of lowercase English letters.
Note: This question is the same as 316: https://leetcode.com/problems/remove-duplicate-letters/