LeetCode 263 Ugly Number

Problem:

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.

Summary:

判断一个数是不是ugly number，即质因子只有2、3、5的数。

Analysis:

判断方法即为不断除以2、3、5，看最终能否得到1。以下两种方法大同小异。

class Solution {
public:
    bool isUgly(int num) {
        if (num <= 0) return false;
        
        while (num != 1) {
            if (num % 2 == 0) num /=2;
            else if (num % 3 == 0) num /=3;
            else if (num % 5 == 0) num /= 5;
            else return false;
        }
        
        return true;
    }
};

class Solution {
public:
    bool isUgly(int num) {
        if (num <= 0) return false;
        
        while (num >= 2 && num % 2 == 0) num /= 2;
        while (num >= 3 && num % 3 == 0) num /= 3;
        while (num >= 5 && num % 5 == 0) num /= 5;
        
        return num == 1;
    }
};