Soyo

Day 9 of 30 days Leetcode challenge

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?


Solution

Just use two stacks to resolve, then compare result

class Solution {
    func backspaceCompare(_ S: String, _ T: String) -> Bool {
        return resolve(S) == resolve(T)
    }
    
    func resolve(_ str: String) -> String {
        var result = ""
        for c in str {
            if c != "#" { result.append(c) }
            else {
                if result.isEmpty { continue }
                result.removeLast()
            }
        }
        return result
    }
}

For O(1) space, I'm thinking about move backward...

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