https://leetcode.com/problems/powx-n/description/
class Solution { public: double myPow(double x, int n) { return helper(x, n); } double helper(double x, long n) { if (n == 0) return 1; if (n < 0) return 1 / helper(x, -n); return n % 2 == 0 ? helper(x * x, n / 2) : x * helper(x, n-1); } };
原文：https://www.cnblogs.com/JTechRoad/p/9060091.html