[LeetCode 263] Ugly Number

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.

Diffculty
Easy

Similar Problems
[LeetCode 136] Happy Number Easy [LeetCode 137] Count Primes Easy [LeetCode 137] Ugly Number II Medium

Analysis

这题简单。既然已经说了ugly number是{2,3,5}的组合乘积构成的， 那么判断逻辑也就简单了，对于任意一个给定的数字，拼命除这三个因子， 最后能整除的就是ugly number，否则就不是。

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; } };