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g0001_0100.s0050_powx_n.Solution Maven / Gradle / Ivy

package g0001_0100.s0050_powx_n;

// #Medium #Top_Interview_Questions #Math #Recursion #Udemy_Integers
// #2022_06_16_Time_1_ms_(82.34%)_Space_43.6_MB_(23.70%)

/**
 * 50 - Pow(x, n)\.
 *
 * Medium
 *
 * Implement [pow(x, n)](http://www.cplusplus.com/reference/valarray/pow/), which calculates `x` raised to the power `n` (i.e., 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
 *
 * **Explanation:** 2\-2 = 1/22 = 1/4 = 0.25 
 *
 * **Constraints:**
 *
 * *   `-100.0 < x < 100.0`
 * *   -231 <= n <= 231-1
 * *   -104 <= xn <= 104
**/
public class Solution {
    public double myPow(double x, int n) {
        long nn = n;
        double res = 1;
        if (n < 0) {
            nn *= -1;
        }
        while (nn > 0) {
            if (nn % 2 == 1) {
                nn--;
                res *= x;
            } else {
                x *= x;
                nn /= 2;
            }
        }
        if (n < 0) {
            return 1.0 / res;
        }
        return res;
    }
}