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

class Solution:
    def canTransform(self, start, end):
        """
        :type start: str
        :type end: str
        :rtype: bool
        """
        if len(start)!=len(end):
            return False
        l = len(start)
        i = j = 0
        while i<l and j<l:
            while j<l and end[j]=='X':
                j += 1              #去掉X
            while i<l and start[i]=='X':
                i += 1             #去掉X
            if i==l and j==l:           #都走到最后
                break
            if i==l or j==l or end[j]!=start[i]:   #只有一方走到最后、或者R对应上了L
                return False
            if start[i]=='L' and i<j:   #L只能向左走
                return False
            if start[i]=='R' and i>j:     #R只能向右走
                return False
            j += 1
            i += 1
        return True