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# Solution 1 simulation

* t-complexity: $O(n + C)$ C is size of charset
* s-complexity: $O(C)$

直接暴力会超时

* s 和 goal 长度或者词频不同，则不为 buddy string
* s 与 goal 不同的字符数量为 2 （能相互交换）
* s and goal diff char number is 0, and s has char which appear more than twice