87. Scramble String Leetcode Python

Given a string s1, we may represent it as a binary tree by partitioning it to two non-empty substrings recursively.
Below is one possible representation of s1 =  "great" :

    great
   /    \
  gr    eat
 / \    /  \
g   r  e   at
           / \
          a   t

To scramble the string, we may choose any non-leaf node and swap its two children.
For example, if we choose the node  "gr"  and swap its two children, it produces a scrambled string  "rgeat" .

    rgeat
   /    \
  rg    eat
 / \    /  \
r   g  e   at
           / \
          a   t

We say that  "rgeat"  is a scrambled string of  "great" .
Similarly, if we continue to swap the children of nodes  "eat"  and  "at" , it produces a scrambled string  "rgtae" .

    rgtae
   /    \
  rg    tae
 / \    /  \
r   g  ta  e
       / \
      t   a

We say that  "rgtae"  is a scrambled string of  "great" .
Given two strings s1 and s2 of the same length, determine if s2 is a scrambled string of s1.
This problem can be solved with brute Force.

class Solution:
    # @param s1, a string
    # @param s2, a string
    # @return a boolean
    def isScramble(self, s1, s2):
        n, m = len(s1),len(s2)
        if n!=m or sorted(s1)!=sorted(s2):
            return False
        if n < 4 or s1 == s2:
            return True
        for i in range(1, n):
            if (self.isScramble(s1[:i],s2[:i]) and self.isScramble(s1[i:], s2[i:]) )or (self.isScramble(s1[:i], s2[-i:]) and self.isScramble(s1[i:], s2[:-i]) ):
                return True
        return False