Implement Pow(x,n)

// http://leetcode.com/onlinejudge#question_50
// Implement pow(x,n)

#include <cfloat>

class Solution {
public:
    bool eq(const double & x, const double & y)
    {
        return std::abs(x-y) < 0.000001;
    }
    double pow(double x, int n) {
        return pow0(x,n);
    }
    double pow0(double x, int n) {
        if(n==0) { return 1.0; }
        if(eq(x, 0.0) || eq(x,1.0) || n==1 ) { return x; }
        if(eq(x, -1.0))
        {
            if(n%2 == 0) { return 1.0; }
            else { return -1.0; }
        }
        if(n<0) { return 1.0/pow0(x,-n); }

        const double y = pow0(x,n/2);
        double r = y * y;
        if(n%2 != 0)  { r *= x; }
        return r;
    }
};