LeetCode C++ 263. Ugly Number【Math】简单

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: [−2³¹, 2³¹ − 1].

题意：编写一个程序判断给定的数是否为丑数。丑数就是只包含质因数 2, 3, 5 的正整数。

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解法

不断整除 2, 3, 5 ，最后判断是否等于 1 。注意，负数和零都不是丑数，一是丑数。具体代码如下：

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; } };

效率如下：

执行用时：0 ms, 在所有 C++ 提交中击败了100.00% 的用户 内存消耗：5.8 MB, 在所有 C++ 提交中击败了39.39% 的用户