50. Pow(x, n) (Medium)

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

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]

Hints

Solutions

class Solution {
    public double myPow(double x, int n) {
        if (n == 0) return 1D;
        long N = n; //use long to avoid overflow.
        return solve(n < 0 ? (1 / x) : x, N < 0 ? (N * -1) : N);
    }

    public double solve(double x, long n) {
        if (n == 1) return x;
        double val = solve(x, n / 2);
        return val * val * ((n % 2) == 0 ? 1 : x);
    }
}
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