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844. Backspace String Compare

Difficulty Topics

Description

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?

Solution

backspace-string-compare.py
class Solution:
    def backspaceCompare(self, s: str, t: str) -> bool:

        def check(A):
            stack = []

            for x in A:
                if x == '#':
                    if stack:
                        stack.pop()
                else:
                    stack.append(x)

            return stack

        return check(s) == check(t)