数学O（1）法
剪绳子
http://www.nowcoder.com/questionTerminal/57d85990ba5b440ab888fc72b0751bf8
class Solution {
public:
int cutRope(int number) {
int tmp = number % 3;
if(number < 4) return number-1;
switch(tmp){
case 0:
return pow(3,number/3);
case 1:
return 4*pow(3,(number-4)/3);
case 2:
return 2*pow(3,number/3);
}
}
};
