263 - Ugly Number

gly 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.

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

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(E) Happy Number (E) Count Primes (M) Ugly Number II

比较直接的一道题，如果不能被2,3,5整除，那肯定不会是，
因为它极有可能是一个更大的质数，例如11，或者仅仅以更大的质数为因子的数字，例如49。
如果能被其中某一个整除，那就用商来继续做判断，直到商小于等于5停止循环。
最后注意负数不算。

class Solution {
public:
    bool isUgly(int num) {
        while(num>5)
        {
            if((num%2)&&(num%3)&&(num%5))
                return false;

            if(0==num%2)
                num /=2;
            if(0==num%3)
                num /=3;
            if(0==num%5)
                num /=5;
        }
        return (num>0);
    }
};
8 ms.