LeetCode 第 263 题 (Ugly Number)

LeetCode 第 263 题 (Ugly Number)

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.

如果一个整数的质因子只有 2,3,5 ,那么这个数称为 Ugly Number。另外, 1 也被认为是 Ugly Number。

这道题比较简单,但是想要一次做对也要仔细考虑清楚各种情况。最开始,我的代码写成了这样:

bool isUgly(int num)
{ while(num % 2 == 0) { num /= 2; }
    while(num % 3 == 0)
    { num /= 3; }
    while(num % 5 == 0)
    { num /= 5; }
    return num == 1;
}

提交之后发现竟然超出时间限制了。仔细想想,当 num = 0 时,代码中的每一个 while 循环都是死循环。所以还要加一句:

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;
}

这样代码就没有问题了。

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