Given two strings `s` and `t`, return `true` if they are equal when both are typed into empty text editors. `'#'` means a backspace character.

Note that after backspacing an empty text, the text will continue empty.

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 = "b"
    Output: false
    Explanation: s becomes "c" while t becomes "b".

Constraints:

- `1 <= s.length, t.length <= 200`
- `s` and `t` only contain lowercase letters and `'#'` characters.

Follow up: Can you solve it in `O(n)` time and `O(1)` space?