# Backspace String Compare

#1

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.

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

#2

The solution below uses a stack.

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

private String getFinalStr(String s){
Stack<Character> stack = new Stack<>();
for(char c : s.toCharArray()){
if(c!='#'){
stack.push(c);
} else{
if(!stack.isEmpty()) stack.pop();
}
}

StringBuilder res = new StringBuilder();
while(!stack.isEmpty()){
res.insert(0, stack.pop());
}
return res.toString();
}
}
``````