844. Backspace String Compare

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. 1 <= S.length <= 200
2. 1 <= T.length <= 200
3. S and T only contain lowercase letters and '#' characters.

Follow up:

• Can you solve it in O(N) time and O(1) space?

class Solution {

public:

    string process (string S) {

        int i = 0, j = 0;

        while (i < S.size()) {

            if (S[i] == '#') {

                if (j > 0) {

                    j--;

                }

                i++;

            } else {

                S[j++] = S[i++];

            }

        }

        if (j == S.size()) {

            return S;

        }

        return S.substr(0, j);

    }

    bool backspaceCompare(string S, string T) {

        if (S == T) {

            return true;

        }

        return process(S) == process(T);

    }

};