[LeetCode] 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 = "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 <= 105
• s consists of lowercase English letters and stars *.
• The operation above can be performed on s.

从字符串中移除星号。

给你一个包含若干星号 * 的字符串 s 。

在一步操作中，你可以：

选中 s 中的一个星号。
移除星号 左侧 最近的那个 非星号 字符，并移除该星号自身。
返回移除 所有 星号之后的字符串。

注意：

生成的输入保证总是可以执行题面中描述的操作。
可以证明结果字符串是唯一的。

来源：力扣（LeetCode）
链接：https://leetcode.cn/problems/removing-stars-from-a-string
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

思路是 stack。如果遇到字母则入栈；遇到星号的时候，如果栈内有字母则弹出，没有字母则可以直接丢弃星号。

时间O(n)

空间O(n)

Java实现

 1 class Solution {
 2     public String removeStars(String s) {
 3         Deque<Character> stack = new ArrayDeque<>();
 4         for (char c : s.toCharArray()) {
 5             if (c == '*') {
 6                 if (!stack.isEmpty()) {
 7                     stack.pollLast();
 8                 }
 9             } else {
10                 stack.offerLast(c);
11             }
12         }
13         StringBuilder sb = new StringBuilder();
14         while (!stack.isEmpty()) {
15             sb.append(stack.pollFirst());
16         }
17         return sb.toString();
18     }
19 }

LeetCode 题目总结