leetcode 50. Pow(x, n) 快速幂

Implement pow(x, n), which calculates x raised to the power n (xn).

Example 1:

Input: 2.00000, 10
Output: 1024.00000
Example 2:

Input: 2.10000, 3
Output: 9.26100
Example 3:

Input: 2.00000, -2
Output: 0.25000
Explanation: 2-2 = 1/22 = 1/4 = 0.25
Note:

-100.0 < x < 100.0
n is a 32-bit signed integer, within the range [−231, 231 − 1]

class Solution {
public:
    // const double eps=1e-5;
    double myPow(double x, long long n) {
        // if(fabs(x-1)<eps)return x;
        if(n==0)return 1;
        bool sign=false;
        if(n<0){
            sign=true;
            n=-n;
        }
        double res=1,base=x;
        while(n){
            if(n&1)res*=base;
            base=base*base;
            n>>=1;
        }
        if(sign)res=1/res;
        return res;
    }
};