Pow(x, n)

直接计算超时

二分法 O(lgn)

public class Solution {
    public double pow(double x, int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(n == 0)
            return 1;
        if(n == 1)
            return x;
            
        boolean negative = false;
        if(n < 0)
            negative = true;
        n = Math.abs(n);
        double result = 0;
        result = pow(x, n>>1);
        result *= result;
        if((n&1) > 0)
            result *= x;
        return negative?1/result:result;
        
    }
}