数值的整数次方.txt

/*

当n为偶数，a^n =（a^n/2）*（a^n/2）
当n为奇数，a^n = a^[(n-1)/2] * a^[(n-1)/2] * a
  举例： 
      2^11 = 2^1 * 2^2 * 2^8
      2^1011 = 2^0001 * 2^0010 * 2^1000
*/
class Solution {
public:
    double Power(double base, int exponent) {
      if(base==0.0) return 0.0; 
      long long p = abs((long long)exponent);
      double r = 1.0;
        while(p){
            if(p & 1) r *= base;
            base *= base;
            p >>= 1;
        }
        return exponent < 0 ? 1/r : r;
    }
};