Leetcode 326. Power of Three

Power of Three - LeetCode

[Easy]

Given an integer n, return true if it is a power of three. Otherwise, return false.

An integer n is a power of three, if there exists an integer x such that n == 3x.

Example 1:

Input: n = 27
Output: true

Example 2:

Input: n = 0
Output: false

Example 3:

Input: n = 9
Output: true

Example 4:

Input: n = 45
Output: false

Follow up: Could you solve it without loops/recursion?

[Gary- recursion]

First answer in Java.

Think:

1. check 0 and 1 corner case.
2. recursion loop n and make sure there is no MOD exist and become 1 at the end
3. can add another line to count how many times it loops

Another recursion answer using two lines:

Basically, it’s the same method but more short.

[Second- brute force Java]

Using HashSet or Array to list all the possible ture answer.

notes: Arrays.binarySearch will return the index of searching result. If no exist in the array, it will return -1.

use array as list in Hashset, and check if result n contains in hashset.

[Third- using Log10, Log3]

notes: have to put log10, instead of log. There will be minor error. And this solution is math solution.