[LeetCode] Pow(x, n)

Implement pow(x, n).

用二分法，O(logn)。注意n < 0的处理

class Solution {
public:
    double power(double x, int n)
    {
        if (n == 0)
            return 1;
            
        double v = power(x, n / 2);
            
        if (n % 2 == 0)
            return v * v;
        else
            return v * v * x;
    }
    
    double pow(double x, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (n < 0)
            return 1.0 / power(x, -n);
        else
            return power(x, n);       
    }
};