leetcode 50. Pow(x, n)

Implement pow(x, n).

Example 1:

Input: 2.00000, 10
Output: 1024.00000
Example 2:

Input: 2.10000, 3
Output: 9.26100

快速幂直接搞，注意边界。

class Solution {
public:
    double pow(double a, long long n) {
        double tmp = 1.0;
        if (a == 1) return 1;
        if (n == 0) return 1;
        if (n == 1) return a;
        else {
            if (n % 2 == 1) {
                tmp = pow(a, (n-1)/2);
                return tmp * a * tmp;
            } else {
                tmp = pow(a, n/2);
              return  tmp*tmp;
            }
        }
    }
    double Pow(double a, long long n){	
	    double ans = 1.0;
    	while(n) {
		    if (n%2 == 1) {
			    ans *= a;
		    }
		    a *= a;
		    n >>= 1;
	    }
	    return ans;
    }
    double myPow(double x, int n) {
        if (n < 0) {
             long long k = n;
            return 1.0/pow(x, -k);
        }
        return pow(x, n);
    }
};