LeetCode[263] Ugly Number（Java）

Problem：

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.

Thought1：

prime number ? return true : prime factorization

Java Solution1

    public boolean isUgly(int num) {        // corner case              if (num < 1) {            return false;        }        // whether the number is a prime number        boolean isPrime = true;             for (int i = 2; i <= Math.sqrt(num); i++) {            if (i > 5) {                return false;            } else if (num % i == 0) {                isPrime = false;                break;            }        }        if (isPrime) {            return num <= 5 ? true : false;        }        // decompose to prime factors        for(int i = 2; i <= num; i++){            if (i > 5) {                return false;            } else if (num % i == 0) {                num /= i;                i--;            }        }        return true;    }

Thought2：

num % 2, 3, 5, respectively until num becomes 1, returnThis method is very effective, since num declines exponentially!

Java Solution2

    // other method to solve this problem on the Internet    public boolean isUgly1(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;        if (num == 1) {            return true;        } else {            return false;        }    }

Online Judge: Ugly Number

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