50. Pow(x, n) (JAVA)

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]

通过二分法，通过平方，减少乘法的次数。

注意指数是负数的情况。

class Solution {
    public double myPow(double x, int n) {
        if(n==0) return 1;
        
        double result = myPow(x, n/2);
        result *= result; 
        if(n%2 == 1) result *= x;
        else if(n%2==-1) result = (1/x) * result; //negative number
        return result;
    }
}