2390. Removing Stars From a String

Description

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 "leet**cod*e". s becomes "lee*cod*e".
- The closest character to the 2nd star is 'e' in "lee*cod*e". 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 <= 10^5
  • s consists of lowercase English letters and stars *.
  • The operation above can be performed on s.

Solution

Code (Rust)

impl Solution {
    pub fn remove_stars(s: String) -> String {
        let mut v = vec![];

        for &b in s.as_bytes(){
            if b == 42 {
                v.pop();
            }else{
                v.push(b);
            }
        }

        return String::from_utf8(v).unwrap();
    }
}

Complexity

  • n the length of s

Time Complexity

  • \(T(n) = \Theta(n)\)

Auxiliary Space

  • \(S(n) = O(1)\)
    • The stack will be consumed by the returned string. Therefore, cost constant space.