2434 - Using a Robot to Print the Lexicographically Smallest String.

Medium

You are given a string s and a robot that currently holds an empty string t. Apply one of the following operations until s and t are both empty:

• Remove the first character of a string s and give it to the robot. The robot will append this character to the string t.

• Remove the last character of a string t and give it to the robot. The robot will write this character on paper.

Return the lexicographically smallest string that can be written on the paper.

Example 1:

Input: s = "zza"

Output: "azz"

Explanation: Let p denote the written string.

Initially p="", s="zza", t="".

Perform first operation three times p="", s="", t="zza".

Perform second operation three times p="azz", s="", t="".

Example 2:

Input: s = "bac"

Output: "abc"

Explanation: Let p denote the written string.

Perform first operation twice p="", s="c", t="ba".

Perform second operation twice p="ab", s="c", t="".

Perform first operation p="ab", s="", t="c".

Perform second operation p="abc", s="", t="".

Example 3:

Input: s = "bdda"

Output: "addb"

Explanation: Let p denote the written string.

Initially p="", s="bdda", t="".

Perform first operation four times p="", s="", t="bdda".

Perform second operation four times p="addb", s="", t="".

Constraints:

• <code>1 <= s.length <= 10⁵</code>

• s consists of only English lowercase letters.