50. Pow(x, n)

Implement pow(x, n), which calculates x raised to the power n (i.e., xn).

Example 1:

Input: x = 2.00000, n = 10 Output: 1024.00000

Example 2:

Input: x = 2.10000, n = 3 Output: 9.26100

Example 3:

Input: x = 2.00000, n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25

Constraints:

• -100.0 < x < 100.0
• -231 <= n <= 231-1
• n is an integer.
• Either x is not zero or n > 0.
• -104 <= xn <= 104

class Solution {
public:
    double myPow(double x, int n) {
        if(n == 0) return 1;
        double half = myPow(x, n / 2);
        if(n % 2 == 0) return half * half;
        // 如果不是偶數的話
        return n > 0 ? half * half * x : half * half / x;
    }
};

• T: $O(\log N)$
• S: $O(1)$