LeetCode: 263. Ugly Number

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LeetCode: 263. 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: [−2^31, 2^31 − 1].

解题思路 —— 递归求解

如果能 num 被 2, 3, 5, 整除， 则 isUgly(num) == isUgly(num/x)，其中 x = 2 或 3 或 5

AC 代码

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