50. Pow(x, n) 求x的n次方

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]
 

求x的n次方,利用递归这班计算

 double myPow3(double x,int n){
    if (n==0) return 1;
    double half = myPow3(x, n/2);
    if (n%2==0) return half*half;
    if (n>0) return half*half*x;
    return half*half/x;
}
 
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