How to get the smallest in lexicographical order?

Question

I am doing a leetcode exercise

https://leetcode.com/problems/remove-duplicate-letters/

The question is:

# Given a string which contains only lowe         


        

Answer 1

You cannot reorder characters. You can only choose which occurrence to remove in case of duplicated characters.

bcabc

We can remove either first b or second b, we can remove either first c or second c. All together four outputs:

..abc
.cab.
b.a.c
bca..

Sort these four outputs lexicographically (alphabetically):

abc
bac
bca
cab

And take the first one:

abc