/*
 * @lc app=leetcode id=50 lang=java
 *
 * [50] Pow(x, n)
 */

// @lc code=start

import java.util.Map;

class Solution {
    public double myPow(double x, int n) {
        Map<Long, Double> track = new HashMap<>();
        long m = n;
        return m>=0?myPow(x, m, track):1/myPow(x, -m, track);
    }

    private double myPow(double x, long n, Map<Long, Double> track) {
        if(n < 0) {
            throw new RuntimeException("not supported number");
        } else if(n <= 1) {
            return n==0?1:x;
        } else if(track.containsKey(n)) {
            return track.get(n);
        }
        long l = n / 2;
        double r = myPow(x, l, track) * myPow(x, n-l, track);
        track.put(n, r);
        return r;
    }
}
// @lc code=end