BackspaceStringCompare.java

/* 844. Backspace String Compare - (https://leetcode.com/problems/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.

 * -------Two pointer approach-------
*/

public class BackspaceStringCompare {
    public boolean backspaceCompare(String S, String T) {
        int i = S.length() - 1;
        int j = T.length() - 1;
        int countS = 0;
        int countT = 0;
        while (i >= 0 || j >= 0) {
            while (i >= 0 && (countS > 0 || S.charAt(i) == '#')) {
                if (S.charAt(i) == '#')
                    countS++;
                else
                    countS--;
                i--;
            }
            char left = i < 0 ? '@' : S.charAt(i);
            while (j >= 0 && (countT > 0 || T.charAt(j) == '#')) {
                if (T.charAt(j) == '#')
                    countT++;
                else
                    countT--;
                j--;
            }
            char right = j < 0 ? '@' : T.charAt(j);
            if (left != right)
                return false;
            i--;
            j--;
        }
        return true;
    }
}