LeetCode-Backspace String Compare

Description：

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?

Java

class Solution {
    public boolean backspaceCompare(String S, String T) {
        return removeBackspace(S).equals(removeBackspace(T));
    }
    private String removeBackspace(String s) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '#') {
                if (sb.length() == 0) continue;
                sb.deleteCharAt(sb.length() - 1);
            } else {
                sb.append(s.charAt(i));
            }
        }
        return sb.toString();
    }
}