backspace-string-compare

Backspace String Compare

LeetCode #: 844

Difficulty: Easy

Topics: Two Pointers, Stack.

Problem

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 <= S.length <= 200
• 1 <= 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 Explanation

The solution uses a two-pointer approach and performs the character comparison from the back of the strings.

If there is a # character, it will loop and skip towards the start of the string accordingly.

As soon as the string comparison fail, it will return false and exit immediately.

Complexity Analysis

Time complexity: O(length of S + length of T)

Space complexity: O(1)