[LeetCode] 2390. Removing Stars From a String [Java]

2390. Removing Stars From a String

You are given a string s, which contains stars *.

In one operation, you can:

• Choose a star in s.
• Remove the closest non-star character to its left, as well as remove the star itself.

Return the string after all stars have been removed.

Note:

• The input will be generated such that the operation is always possible.
• It can be shown that the resulting string will always be unique.

Example 1:

Input: s = "leetcode"
*Output: "lecoe"
Explanation: Performing the removals from left to right:

• The closest character to the 1st star is 't' in "leet**code". s becomes "leecod*e".
• The closest character to the 2nd star is 'e' in "lee*code". s becomes "lecode".
• The closest character to the 3rd star is 'd' in "lecod*e". s becomes "lecoe".
  There are no more stars, so we return "lecoe".

Example 2:

Input: s = "erase***"
**Output: ""
Explanation: The entire string is removed, so we return an empty string.

Constraints:

• 1 <= s.length <= 105
• s consists of lowercase English letters and stars *.
• The operation above can be performed on s.

---

어렵지는 않은 문제였다. 문자열을 순회하면서 *를 만나면 직전(왼쪽)에 있는 문자를 삭제하면 된다.
스택 자료구조를 이용해서 풀고자 했고, 구현은 Deque 클래스를 사용했다.

문자를 하나씩 순회하면서 다음 두 가지 case로 작업해주면 된다.

1. If the current character c is *, the top element of the stack is removed.
2. If the current character c is not *, the character is pushed onto the stack.

코드는 다음과 같다.

class Solution {
    public String removeStars(String s) {
        Deque<Character> dq = new ArrayDeque<>();

        for(int i=0; i<s.length(); i++){
            char c = s.charAt(i);

            if(c!='*'){
                dq.addLast(c);
                continue;
            }

            if(!dq.isEmpty()){
                dq.removeLast();
            }
        }

        StringBuilder result = new StringBuilder();
        for(char c : dq){
            result.append(c);
        }

        return result.toString();
    }
}