Added backspace string compare solution (#340)

Author: Aiyan-Faras

Java/String/BackspaceStringCompare.java

@@ -0,0 +1,41 @@
+/* 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;
+    }
+}