LeetCode 844. Backspace String Compare

Description

https://leetcode.com/problems/backspace-string-compare/

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.

Follow up:

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

Explanation

Create a helper function to compare if the backspace results from two strings are matched.

Python Solution

class Solution:
    def backspaceCompare(self, S: str, T: str) -> bool:
        
        def helper(s):
            result = []

            for c in s:
                if c != '#':
                    result.append(c)
                elif result:
                    result.pop()
        
            return "".join(result)
            
        return helper(S) == helper(T)
  • Time complexity: O(n).
  • Space complexity: O(n).

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