題目描述(Medium)

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

題目連結

https://leetcode.com/problems/powx-n/description/

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]

演算法分析

二分法，

提交程式碼：

class Solution {
public:
    double myPow(double x, int n) {
        if (n < 0) return power(1/x, n);
        return power(x, n);
    }
    
private:
    double power(double x, int n) {
        if (n == 0) return 1;
        double v = power(x, n / 2);
        if (n % 2 == 0) return v * v;
        else
            return v * v * x;
    }
};