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

clearly, the wanted output must contain only letter once. now, from what i understand, you must pick the letters in a manner that will give you the best order when the leftmost letters come before in (abc? ascii?) now you'd ask why "acdb" than and not "abcd". i think you don't take the first "cb" since you more c and b later, but you're have to take the "a" since there's only one coming now. then you must take c 'cause there are no more "d" after the next b. that's why you take c, and then d because no more d's later.

in short, you want to take it with best lexicographical order from low to high, but make sure you take all the letters while iterating over the input string.