LeetCode-Pow(x, n)

Recursive:

public class Solution {
    public double pow(double x, int n) {
        if ( n == 0 )
            return 1;
        double half = pow ( x, n/2);
        double res = 1.0;
        if ( n % 2 == 0 ){
            res = half * half;
        }
        else if ( n > 0)
            res = half * half * x;
        else 
            res = half * half / x;
        return res;
    }
}

Iterative:

public class Solution {
    public double pow(double x, int n) {
        if ( n == 0 )
            return 1;
        double res = 1.0;
        for ( int i = n; i != 0; i/=2 ){
            if ( i % 2 != 0 )
                res *= x;
            x *= x;
        }
        if ( n < 0 )
            res = 1.0/res;
        return res;
    }
}