解题方法主要是利用递归和二分，具体就是把x的n次方划分成两个x的n/2次方相乘，然后递归求解子问题，结束条件是n为0返回1。因为是对n进行二分，所以算法复杂度是O(logn)。(Problem solving method is mainly the use of recursive and two points, specifically the x n side is divided into two X n/2 times multiplication, and then recursively solve sub problems, the end of the condition is N 0, return 1. Because it is two points for N, the algorithm complexity is O (logn).)