题目

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.

解题思路

1. 小于1的不是丑数
2. 大于1的时候，如果能被2整除，就循环除以2，直到不能被2整除；同理对3，5执行同样操作
3. 等于1的话是丑数，不等于1（大于1）说明该数还有其他因子，不是丑数

代码

func isUgly(num int) bool {
    if num < 1 {
        return false
    }

    for ; num > 1 && num % 2 == 0 ; {
        num /= 2
    }

    for ; num > 1 && num % 3 == 0 ; {
        num /= 3
    }

    for ; num > 1 && num % 5 == 0 ; {
        num /= 5
    }

    if num == 1 {
        return true
    }

    return false
}