50. Pow(x, n)
Medium

Implement pow(xn), 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]

 

 

 1 class Solution {
 2 public:
 3     double quick_mul(double x, long long n) {
 4         if (n == 1) return x;
 5         auto res = myPow(x,n/2);
 6         if (n%2==1) {
 7             return res*res*x;
 8         } else {
 9             return res*res;
10         }
11         return 1;
12     }
13     double myPow(double x, int n) {
14         if (n==0) return 1;
15         long long N = n;
16         return N > 0 ? quick_mul(x,N):1/quick_mul(x,-N);
17     }
18 };

 

 

class Solution {
public:
    double myPow(double x, int n) {
        if (n==-2147483648) return Pow(x,n+1)/x;
        else return Pow(x,n);
        
    }
    double Pow(double x, int n) {
        if (x==1.0 || x==0.0) return x;
        if(n > 0) {
            double res = myPow(x,n/2);
            if (n%2==0) return res*res;
            else return res*res*x;
        } else if (n < 0) {
            double res = myPow(x,-n/2);
            if(((-n)%2)==0) return 1/(res*res);
            else return 1/(res*res*x);
        } else {
            return 1;
        }
    }
};

  

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