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 = "#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". 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?