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.
根据丑数的定义,如果一个数能被2整除,我们把它连续除以2;如果能被3整除,就连续除以3,如果能被5整除,就连续除以5。如果最后我们得到的是1,那么这个数就是丑数,否则不是。注意:需要提前判断0是否是丑数,否则会造成死循环。
class Solution { public: bool isUgly(int num) { if (num == 0) return false; while (num % 2 == 0) num /= 2; while (num % 3 == 0) num /= 3; while (num % 5 == 0) num /= 5; return (num == 1) ? true : false; } }; // 3 ms