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Backspace String Compare

Difficulty: Easy

Problem 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.

Key Insights

  • The '#' character represents a backspace, which removes the most recent character typed.
  • We need to simulate the typing process for both strings and compare the final results.
  • A two-pointer technique can be effectively used to traverse both strings from the end to the beginning, skipping characters as necessary.

Space and Time Complexity

Time Complexity: O(n)
Space Complexity: O(1)

Solution

The problem can be solved by using a two-pointer approach where we traverse both strings from the end. For each string, we skip characters that are followed by '#' (indicating backspaces) and compare the resulting characters. The characters are matched until we either finish both strings or find a mismatch.

Code Solutions

def backspaceCompare(s: str, t: str) -> bool:
    def process_string(string):
        skip = 0
        processed = []
        # Traverse the string from the end
        for char in reversed(string):
            if char == '#':
                skip += 1
            elif skip > 0:
                skip -= 1
            else:
                processed.append(char)
        return processed
    
    return process_string(s) == process_string(t)
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