leetcode-326-easy-2

Power of Three

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
Explanation: 27 = 33
Example 2:

Input: n = 0
Output: false
Explanation: There is no x where 3x = 0.
Example 3:

Input: n = -1
Output: false
Explanation: There is no x where 3x = (-1).
Constraints:

-231 <= n <= 231 - 1
Follow up: Could you solve it without loops/recursion?

思路一：暴力计算 3 的 n 次方，和给定的数进行对比

    public static boolean isPowerOfThree(int n) {
        long val = 1;
        while (val < n) {
            val *= 3;
        }

        return val == n;
    }

思路二：看了一下官方题解，有更好的解法

    public boolean isPowerOfThree(int n) {
        while (n != 0 && n % 3 == 0) {
            n /= 3;
        }
        return n == 1;
    }

    public boolean isPowerOfThree(int n) {
        return n > 0 && 1162261467 % n == 0;
    }