2390. Removing Stars From a String

Source

Question: 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 = “leet**cod*e” Output: “lecoe” Explanation: Performing the removals from left to right:

• The closest character to the 1st star is ‘t’ in “lee**t**code”. s becomes “leecod*e”.
• The closest character to the 2nd star is ‘e’ in “leecode”. s becomes “lecod*e”.
• 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.

Solution:

class Solution {
    public String removeStars(String s) {
        Deque<Character> stack = new ArrayDeque<>();
        Deque<Character> finalStack = new ArrayDeque<>();
        char[] loc = s.toCharArray();
 
        int start = loc.length - 1;
        while(start >= 0){
            if(loc[start] == '*'){
                start--;
            } else{
                stack.push(loc[start]);
            }
            start--;
        }
 
        StringBuilder res = new StringBuilder();
        while(!stack.isEmpty()){
            res.append(stack.pop());
        }
        
        return res.toString();
    }
}