[LeetCode] Scramble String

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.

class Solution {
public:
    bool isScramble(string s1, string s2) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        
        if(s1.length() !=s2.length() )
            return false;
        
        //scramble s1 to s2. Partition s1 from 0 to n if the first n elements are the same in s1 and s2 except the order
        //keep a table to match the number of alphebits
        int A[26]={0};
        for(int i=0;i<s1.length();i++)
        {
            A[s1[i]-'a']++;
            A[s2[i]-'a']--;
        }
        for(int i=0;i<s1.length();i++)
            if(A[s1[i]-'a'] != 0)
                return false;
        
        if(s1.length()==1) return true;
        
        //start partitioning
        bool result=false;
        for(int i=1;i<s2.length();i++)
        {
            bool result1=isScramble(s1.substr(0,i),s2.substr(0,i))&&isScramble(s1.substr(i,s1.length()-i),s2.substr(i,s2.length()-i));
            bool result2=isScramble(s1.substr(0,i),s2.substr(s2.length()-i,i)) && isScramble(s1.substr(i,s1.length()-i),s2.substr(0,s2.length()-i));
            
            result=result1||result2;
            if(result==true)
                return result;
        }
        return result;
    }
};