pow(x,n)

class Solution {
public:
double myPow(double x, int n) {
if(n<0)
{
if(n==INT_MIN)
return 1.0/ ( myPow(x,INT_MAX)*x);  //be carefully... INT_MIN=-INT_MAX-1;
else
return 1.0/ myPow(x,-n);
}
if(n==0)
return 1.0;
double ans=1.0;
for(;n;x*=x,n>>=1)
{
if(n&1)
ans*=x;
}
return ans;
}
};