LC: https://leetcode-cn.com/problems/shu-zhi-de-zheng-shu-ci-fang-lcof/
    牛客： https://www.nowcoder.com/practice/1a834e5e3e1a4b7ba251417554e07c00?tpId=13&&tqId=11165&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking

    1. 浮点型 快速幂
    2. 将底数转化为 分数计算，确保指数是正数;
    1. class Solution {
    2. public:
    3.     double myPow(double x, int n) {
    4.         if (x == 1 || n == 0) {
    5.             return 1;
    6.         }
    7.         double sum = 1;
    8.         long num = n;
    9.         if (n < 0) {
    10.             x = 1 / x;
    11.             num = -num;
    12.         }
    13.         while (num) {
    14.             if (num & 1) {
    15.                 sum *= x;
    16.             }
    17.             num >>= 1;
    18.             x *= x;
    19.         }
    20.         return sum;
    21.     }
    22. };