428. Pow(x, n)【medium】

Implement pow(x, n).

Notice

You don't need to care about the precision of your answer, it's acceptable if the expected answer and your answer 's difference is smaller than 1e-3.

 

Example

Pow(2.1, 3) = 9.261
Pow(0, 1) = 0
Pow(1, 0) = 1

Challenge

O(logn) time

参考了@grandyang 的代码

解法一：

 class Solution {
 public:
     double myPow(double x, int n) {
         double res = 1.0;
         for (int i = n; i != ; i /= ) {
             if (i %  != ) {
                 res *= x;
             }
             x *= x;
         }
         return n <  ?  / res : res;
     }
 };        

迭代

解法二：

 class Solution {
 public:
     double myPow(double x, int n) {
         if (n < ) {
             return  / power(x, -n);
         }

         return power(x, n);
     }
     double power(double x, int n) {
         if (n == ) {
             return ;
         }

         double half = power(x, n / );
         if (n %  == ) {
             return half * half;
         }

         return x * half * half;
     }
 };

解法三：

 class Solution {
 public:
     /**
      * @param x the base number
      * @param n the power number
      * @return the result
      */
     double myPow(double x, int n) {
         if (n == ) {
             return ;
         }
         if (n == ) {
             return x;
         }
         if (n == -) {
             return  / x;
         }

         return myPow(x, n / ) * myPow(x, n - n / );
     }
 };

会超时