50 Pow(x, n)

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 double myPow(double x, int n) {
        if (n == 0) {
            return 1;
        }
        if (n == 1) {
            return x;
        }
        long pow = Math.abs((long)n);
        double result = 1;
        while (pow > 0 ) {
            if (pow % 2 != 0) {
                result *= x;
            }
            x *= x;
            pow /= 2;
        }
        if (n < 0) {
            return 1.0 / result;
        }
        return result;
    }
}

class Solution {
    public double myPow(double x, int n) {
        if(n > 0) {
            return pow(x, n);
        } else {
            return 1.0 / pow(x, -n);
        }
    }
    public double pow(double x, int n) {
        if (n == 0) {
            return 1;
        }
        double y = pow(x, n / 2);
        if (n % 2 == 0) {
            return y * y;
        } else {
            return y * y * x;
        }
    }
}