# 844     Backspace String Compare

## 844. [Backspace String Compare](https://leetcode.com/problems/backspace-string-compare/description/)

## 1. Question

Given two strings `S` and`T`, return if they are equal when both are typed into empty text editors.`#`means a backspace character.

**Example 1:**

```
Input: S = "ab#c", T = "ad#c"
Output: true

Explanation: Both S and T become "ac".
```

**Example 2:**

```
Input: S = "ab##", T = "c#d#"
Output: true

Explanation: Both S and T become "".
```

**Example 3:**

```
Input: S = "a##c", T = "#a#c"
Output: true

Explanation: Both S and T become "c".
```

**Example 4:**

```
Input: S = "a#c", T = "b"
Output: false

Explanation: S becomes "c" while T becomes "b".
```

**Note**:

1. `1 <= S.length <= 200`
2. `1 <= T.length <= 200`
3. `S`and`T`only contain lowercase letters and`'#'`characters.

**Follow up:**

* Can you solve it in`O(N)`time and`O(1)`space?

## 2. Implementation

**(1) Stack**

思路: 用StringBuilder模拟stack的操作，当遇到"#"而且stringbuilder不为空时，将最后一个character删除

```java
class Solution {
    public boolean backspaceCompare(String S, String T) {
        return getString(S).equals(getString(T));
    }

    public String getString(String s) {
        StringBuilder res = new StringBuilder();

        for (char c : s.toCharArray()) {
            if (c != '#') {
                res.append(c);
            }
            else if (res.length() > 0) {
                res.deleteCharAt(res.length() - 1);
            }
        }
        return res.toString();
    }
}
```

## 3. Time & Space Complexity

**(1) Stack：** 时间复杂度O(n), 空间复杂度O(1)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://protegejj.gitbook.io/oj-practices/chapter1/stack/844-backspace-string-compare.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.