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.

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 = "#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?

Code

class Solution {
    public boolean backspaceCompare(String S, String T) {
        int indexS = S.indexOf('#');
        int indexT = T.indexOf('#');
        while (indexS != -1) {
            S = indexS == 0 ? S.substring(indexS + 1) : S.substring(0, indexS - 1) + S.substring(indexS + 1);
            indexS = S.indexOf('#');
        }
        while (indexT != -1) {
            T = indexT == 0 ? T.substring(indexT + 1) : T.substring(0, indexT - 1) + T.substring(indexT + 1);
            indexT = T.indexOf('#');
        }
        return S.equals(T);
    }
}