两个string 都有字母和backspace，然后看最后是不是一样的结果
从后往前traverse O(N) + O(1)
class Solution {
public boolean areSameStrings(String s1, String s2) {
if (s1 == null || s2 == null) {
return false;
}
if (s1.equals(s2)) {
return true;
}
int i = s1.length() - 1;
int j = s2.length() - 1;
while (i >= 0 && j >= 0) {
while (s1.charAt(i) == '$') {
i -= 2;
}
while (s2.charAt(j) == '$') {
j -= 2;
}
if (s1.charAt(i) != s2.charAt(j)) {
return false;
}
i--;
j--;
} // end of while
if (i != -1 || j != -1) {
return false;
}
return true;
}
}
