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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]

*/

public class PowXN50 {

/**

* https://leetcode.com/problems/powx-n/solution/

*/

public double myPow(double x, int n) {

long N = n;

if (N < 0) {

x = 1 / x;

N = -N;

}

return fastPow(x, N);

}

private double fastPow(double x, long n) {

if (n == 0) {

return 1.0;

}

double half = fastPow(x, n / 2);

if (n % 2 == 0) {

return half * half;

} else {

return half * half * x;

}

}

/**

* https://leetcode.com/problems/powx-n/solution/

*/

public double myPow2(double x, int n) {

long N = n;

if (N < 0) {

x = 1 / x;

N = -N;

}

double ans = 1;

double current_product = x;

for (long i = N; i > 0; i /= 2) {

if ((i % 2) == 1) {

ans = ans * current_product;

}

current_product = current_product * current_product;

}

return ans;

}

}