LeetCode 777. Swap Adjacent in LR String

In a string composed of ‘L’, ‘R’, and ‘X’ characters, like “RXXLRXRXL”, a move consists of either replacing one occurrence of “XL” with “LX”, or replacing one occurrence of “RX” with “XR”. Given the starting string start and the ending string end, return True if and only if there exists a sequence of moves to transform one string to the other

Example:

Input: start = "RXXLRXRXL", end = "XRLXXRRLX"
Output: True

Explanation:
We can transform start to end following these steps:
RXXLRXRXL ->
XRXLRXRXL ->
XRLXRXRXL ->
XRLXXRRXL ->
XRLXXRRLX

Note:
1 <= len(start) = len(end) <= 10000.
Both start and end will only consist of characters in {‘L’, ‘R’, ‘X’}.

思路：start裡的R可以先出現，L只能後出現。因此iteration的時候，統計R和L的值，如果i位置時，Rs < Re || Ls > Le，則返回false. 同時用兩個stringbuilder記錄兩個字串，如果相同則返回true，否則返回false.

    public boolean canTransform(String start, String end) {
        if(start.length() != end.length()) return false;
        int r = 0;
        int l = 0;
        StringBuilder s = new StringBuilder();
        StringBuilder e = new StringBuilder();
        for (int i = 0; i < start.length(); i++) {
            char ss = start.charAt(i);
            char ee = end.charAt(i);
            if (ss == 'R') {
                r++;
                s.append(ss);
            } else if (ss == 'L') {
                l++;
                s.append(ss);
            } else {}
            if (ee == 'R') {
                r--;
                e.append(ee);
            } else if (ee == 'L') {
                l--;
                e.append(ee);
            } else {}
            if (r < 0 || l > 0) {
                return false;
            }
        }
        return s.toString().equals(e.toString()) ? true : false;
    }