问题
Write a program to check whether a given number is an ugly number.
Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7.
Note that 1 is typically treated as an ugly number.
例子
175
false
分析
不断用2 3 7除n，如果n在等于1之前除不尽，说明n不是丑数；否则是丑数。
要点
弄清丑数的概念。
时间复杂度
O(logn)
空间复杂度
O(1)
代码
class Solution {
public:
bool isUgly(int num) {
if (num < 1) return false;
while (num > 1) {
if (!(num & 1))
num /= 2;
else if (num % 3 == 0)
num /= 3;
else if (num % 5 == 0)
num /= 5;
else
return false;
}
return true;
}
};
