50.Pow(x, n)

Tags: Medium Math Binary Search

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

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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]

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#include <cmath>
class Solution {
public:
    double myPow(double x, long long n) {
        if(n == 0) return 1.0;
        if(n == 1) return x;
        if(n == -1) return 1.0/x;

        if(n%2 == 0){
            double res = pow(x, n/2);
            return res*res;
        }else{
            double res = pow(x, (n-1)/2);
            return res*res*x;
        }    
    }
};