leetcode之Pow(x, n)

class Solution {
public:
    bool equal(double x, double y) {
        if (abs(x-y) < 0.000001) {
            return true;
        }
        return false;
    }
    double pow(double x, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (equal(x, 0.0) && n <0) {
            return 0.0;
        }
        if (n==0) {
            return 1.0;
        }
        bool negative = false;
        if (n < 0) {
            n = -n;
            negative = true;
        }
        double res = 1.0;
        /*while (n>0) {
            n--;
            res*=x;
        }*/
        res = pow(x, n>>1);
        res *= res;
        if (n&0x01==1)
            res=res*x;
        if (negative) {
            res=1.0/res;
        }
        return res;
    }
};