[LeetCode] Remove Duplicate Letters

문제

1. Given a string s, remove duplicate letters so that every letter appears once and only once. You must make sure your result is the smallest in lexicographical order among all possible results.

   Note: This question is the same as 1081: https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/

예제

Example 1:

Input: s = "bcabc"
Output: "abc"

Example 2:

Input: s = "cbacdcbc"
Output: "acdb"

조건

• 1 <= s.length <= $10^4$
• s consists of lowercase English letters.

답

풀이 1

class Solution:
    def removeDuplicateLetters(self, s: str) -> str:
        stack, seen, counter = [], set(), collections.Counter(s)
        
        for char in s:
            counter[char] -= 1
            
            if char in seen:
                continue
            
            while stack and stack[-1] > char and counter[stack[-1]] > 0:
                seen.remove(stack.pop())
                
            stack.append(char)
            seen.add(char)
       
        return ''.join(stack)
                    

풀이 2

class Solution:
    def removeDuplicateLetters(self, s: str) -> str:
    	# 집합으로 정렬
        for char in sorted(set(s)):
            suffix = s[s.index(char):]
            # 전체 집합과 접미사 집합이 일치할 때 분리 진행
            if set(s) == set(suffix):
                return char + self.removeDuplicateLetters(suffix.replace(char, ''))
        return ''