Given two strings s and t, where # means a backspace, return true if typing each string into an empty text editor produces the same result. Building each string's final contents with a stack works — push regular characters, pop on '#' — but it costs extra storage the size of both inputs. Scanning from the end of each string avoids that: resolve each pointer to the next character that survives every backspace to its right (skipping the '#' itself and however many characters it deletes), then compare those two resolved characters directly. A mismatch — or one string running out before the other — settles the answer immediately, all without ever building a final string.