[LeetCode] Pow(x, n) 二分搜索

class Solution {
public:
    double pow(double x, int n) {
        if(n==0)    return 1;
        bool nNeg = false;
        long long int nn = n;
        if(n<0){
            nn = - nn ;
            nNeg  =true;
        }
        bool xNeg = false;
        if(x<0){
            x = -x;
            if(n%2==1)
                xNeg = true;
        }
        double ret = 1;
        while(nn){
            if(nn&1)
                ret *= x;
            x *=x;
            nn>>=1;
        }
        if(nNeg==true)
            ret = 1/ret;
        if(xNeg==true)
            return -ret;
        return ret;
    }
};