263. Ugly Number*
https://leetcode.com/problems/ugly-number/
题目描述
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
.
Example 1:
Input: 6
Output: true
Explanation: 6 = 2 × 3
Example 2:
Input: 8
Output: true
Explanation: 8 = 2 × 2 × 2
Example 3:
Input: 14
Output: false
Explanation: 14 is not ugly since it includes another prime factor 7.
Note:
- 1 is typically treated as an ugly number.
- Input is within the 32-bit signed integer range: .
C++ 实现 1
思路: 首先要注意输入是有符号整数, 那么负数和 0 都被认为不是 UN. 对于正整数 num, 可以不断地使用 2, 3, 5 对其进行整除, 最后判断 num 是不是等于 1. 如果相等, 说明 num 总是以 2, 3, 5 为质因子, 如果不相等, 那么不是 UN.
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;
}
};