Solution: Remove Duplicate Letters
Explore a stack-based algorithm to remove duplicate letters from a string while ensuring the resulting string is lexicographically smallest. Learn how to track character frequencies, manage a visited set, and use a greedy approach to efficiently build the final unique string. Understand the solution's O(n) time complexity and constant space usage.
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Statement
You are given a string, s, consisting only of lowercase English letters. Your task is to remove duplicate letters so that:
Each letter appears only once in the resulting string.
The resulting string is the smallest in lexicographical order among all possible results that satisfy the above condition.
Return the final string.
A string,
a, is considered lexicographically smaller than stringbif:
In the first position where they differ, the character in
aappears earlier in the alphabet than inb.If
ais a ...