240. Remove Duplicate Letters

Given a string s, remove duplicate letters so that every letter appears exactly once. Return the lexicographically smallest result among all valid orderings that preserve relative feasibility.

Input: A quoted string s.

Output: Quoted string — the smallest unique-letter string.

Examples

Input: "bcabc"
Output: "abc"
Explanation: Smallest with each letter once.

Input: "cbacdcbc"
Output: "acdb"
Explanation: Smallest valid ordering.

Input: "abc"
Output: "abc"
Explanation: Already unique.

Constraints

• 1<=s.length<=10^4
• lowercase letters

Asked by