number-theory/ugly-number
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2023-12-01
Ugly Number
描述
Write a function 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.
分析
思路很简单，把n里面的 2,3,5 全部消掉，看最后能不能剩下 1。
代码
// Ugly Number
// Time complexity: O(logn), Space complexity: O(1)
public class Solution {
public boolean 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;
}
}