（难度Hard）Problem 87. Scramble String（爬行字符串）

### 链接

Scramble String - LeetCode

Hard

### 题干

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.

### 题意

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

### 样例

Example 1:

Input: s1 = “great”, s2 = “rgeat”
Output: true