50. pow (x, n) - fast power

50. Pow(x, n)

Realization pow(x, n) , Computation x The integer of n Power function （ namely ,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
explain ：2-2 = 1/22 = 1/4 = 0.25

The solution code is as follows , Fast power , Usually with a 2 A fast product algorithm with base ：

double myPow(double x, int n){
    
    if (n == 0)
        return 1; //  Recursive export 
    if (n == 1)
        return x; //  Recursive export 
    // if (n < 0)
    // return 1 / myPow(x, -n); //  here n Will cross the border 
    if (n == -1)
        return 1 / x; //  Just define recursive exits 
    if (n % 2 != 0)
        return x * myPow(x, n - 1);
    else
        return myPow(x * x, n / 2);
}