Is Backspace String Compare easy or hard?

Backspace String Compare is classified as an Easy problem. The stack-based simulation is straightforward for beginners, while the two-pointer optimization introduces a useful interview pattern for processing strings in constant space.

Backspace String Compare Python/Java solution

Python and Java implementations typically follow either the stack simulation or the two-pointer approach. The stack solution uses lists or Stack collections to build the final string, while the two-pointer method iterates from the end of the string and compares valid characters without extra storage.

How to solve Backspace String Compare in O(n)?

Traverse both strings from right to left using two pointers. Maintain a skip counter for each string to track pending backspaces. When a '#' appears increase the counter, and when a normal character appears with a positive counter skip it. Compare the next valid characters from both strings until both pointers finish.

What is the best approach for Backspace String Compare?

The optimal approach uses a two-pointer scan from the end of both strings. Each pointer skips characters that are deleted by backspaces using a counter. This method processes each character once, resulting in O(n) time complexity and O(1) extra space, making it more efficient than building new strings.

Is Backspace String Compare asked at Google/Amazon/Meta?

Backspace String Compare is a common interview-style question used by companies such as Amazon, Google, and Meta to test string processing and pointer techniques. It evaluates whether candidates can simulate operations efficiently and optimize space usage.

What data structure is used in Backspace String Compare?

A stack is commonly used to simulate the typing process because it naturally removes the most recently added character when a backspace appears. The optimized solution replaces the stack with two pointers and counters, achieving the same effect with constant extra space.

What is the time complexity of Backspace String Compare?

Both common solutions run in O(n) time where n is the length of the strings. The stack simulation processes every character once while pushing and popping operations. The optimized two-pointer technique also scans each character at most once while skipping deleted characters.

Description Solution Video 7:42

844. Backspace String Compare

Easy49.9% acceptance14 companies

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?

Asked at 14 companies

Roku MicroStrategy Agoda Wells Fargo Wayfair Goldman Sachs

IBM

Google Microsoft Salesforce Amazon Meta

+2 more

Bloomberg Oracle

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7:42

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844. Backspace String Compare

Asked at 14 companies

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