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.

有一种方法叫做简单粗暴。。。

递归+剪枝

bool isScramble(string s1, string s2) {
        // Note: The Solution object is instantiated only once.
    	if(s1.length() != s2.length()) return false;
		if(s1 == s2) return true;

		int A[26] = {0};
		for(int i = 0; i < s1.length(); i++)
			++A[s1[i]-'a'];

		for(int j = 0; j < s2.length(); j++)
			--A[s2[j]-'a'];

		for(int k = 0; k < 26; k++)
			if(A[k] != 0) return false;

        for(int i = 1; i < s1.length(); i++)
		{
			bool result = isScramble(s1.substr(0,i), s2.substr(0,i)) 
				&& isScramble(s1.substr(i), s2.substr(i));
			result = result || (isScramble(s1.substr(0,i), s2.substr(s2.length()-i, i))
				&& isScramble(s1.substr(i), s2.substr(0,s2.length()-i)));
			if(result) return true;
		}
		return false;
    }