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844. Backspace String Compare

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?

Solution:

class Solution {
    public boolean backspaceCompare(String s, String t) {
        StringBuilder sbS = new StringBuilder();
        StringBuilder sbT = new StringBuilder();
        for (int i = 0; i < s.length(); i++){
            if(s.charAt(i) == '#'){
                if (sbS.length() > 0){
                    sbS.deleteCharAt(sbS.length() - 1);
                }
            }else{
                sbS.append(s.charAt(i));
            }
        }

        for (int i = 0; i < t.length(); i++){
            if(t.charAt(i) == '#' ){
                if (sbT.length() > 0){
                    sbT.deleteCharAt(sbT.length() - 1);
                }
            }else{
                sbT.append(t.charAt(i));
            }
        }

        if (sbS.toString().equals(sbT.toString())){
            return true;
        }else{
            return false;
        }
    }
}
// TC: O(n)
// SC: O(n)