Pow(x, n)

Implement pow(x, n).

Runtime: 23ms

class Solution {
public:
    /**
     * @param x the base number
     * @param n the power number
     * @return the result
     */
    double myPow(double x, int n) {
        // Write your code here
        if (x == 0) return 0;
        if (n == 0) return 1;
        if (n == 1) return x;
        if (n == -1) return 1 / x;
        
        double temp = myPow(x, n / 2);
        return temp * temp * myPow(x, n % 2);
    }
};

Analyse: Be aware of corner cases. For exmaple, x = 0, n = 0, n = 1, and n < 0. Note the highlited area, if n == INT_MIN, we have to use braces to ensure the correctness. 

Runtime: 4ms.

class Solution {
public:
    double myPow(double x, int n) {
        if(!x) return 0.0;
        if(!n) return 1.0;
        if(n == 1) return x;
        
        if(n < 0) {
            double temp = myPow(1 / x, -(n / 2));
            return temp * temp * myPow(1 / x, -(n % 2));
        }
        else{
            double temp = myPow(x, n / 2);
            return temp * temp * myPow(x, n % 2);
        }
    }
};