LeetCode#263 Ugly Number (week8)

week8

题目

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.
原题地址：https://leetcode.com/problems/ugly-number/description/

解析

题目要求判断给定的数分解为质数，这些质数是否只包含2，3，5，是返回true，否则返回false。
大致思路是将该数分解为 的形式，其中a，b，c，d为正整数，检查d是否为1，是则质数中只包含2，3，5，返回true，反之返回false。

易错点

题目中明确指明1为ugly number，而0没有说明，容易将其忽略，事实证明0不视为ugly number。在下面编程实现中如果忘记将0特殊考虑则会陷入死循环。

代码

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