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
 = 1/2
2
 = 1/4 = 0.25

Note:

• -100.0 < x < 100.0
• n is a 32-bit signed integer, within the range [−2 31 , 2 31 − 1]

Solution

(1) Java

class Solution {
    public double myPow(double x, int n) {
        if (x == 0) {
            return 0;
        }
        int sign = n >= 0 ? 1 : -1;
        if (n == 0) {
            return (double)sign;
        }
        long nn = (long)n;
        double rst = helper(x, Math.abs(nn));
        return sign > 0 ? rst : 1/rst;
    }

    private double helper(double x, long n) {
        if (n == 1) {
            return x;
        }
        double rst = helper(x, n/2);
        rst *= rst;
        if (n%2 != 0) {
            rst *= x;
        }
        return rst;
    }
}

(2) Python

(3) Scala