LeetCode: 326. Power of Three

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326. Power of Three

LeetCode - Power of Three

发现一个很奇怪的问题：如果通过计算相乘来判断，则会超时；如果通过相除来判断，则能顺利通过。感觉计算量是一样的啊？为什会有这么大的差距啊？

利用对数计算也不失为一个很好的办法！

Given an integer, write a function to determine if it is a power of three.

Example 1:

Input: 27
Output: true

Example 2:

Input: 0
Output: false

Example 3:

Input: 9
Output: true

Example 4:

Input: 45
Output: false

Follow up:

Could you do it without using any loop / recursion?

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/**
 * Runtime: 11 ms, faster than 89.24% of Java online submissions for Power of Three.
 *
 * Memory Usage: 36.4 MB, less than 6.25% of Java online submissions for Power of Three.
 *
 * Copy from: https://leetcode.com/problems/power-of-three/solution/[Power of Three solution - LeetCode]
 */
public boolean isPowerOfThree(int n) {
    return (Math.log10(n) / Math.log10(3)) % 1 == 0;
}
/**
 * Runtime: 11 ms, faster than 89.24% of Java online submissions for Power of Three.
 *
 * Memory Usage: 36.6 MB, less than 6.25% of Java online submissions for Power of Three.
 *
 * Copy from: https://leetcode.com/problems/power-of-three/solution/[Power of Three solution - LeetCode]
 */
public boolean isPowerOfThreeDiv(int n) {
    if (n < 1) {
        return false;
    }
    while (n % 3 == 0) {
        n /= 3;
    }
    return n == 1;
}

/**
 * Time Limit Exceeded
 */
public boolean isPowerOfThreeMult(int n) {
    if (n < 1) {
        return false;
    }
    int temp = 1;
    for (int i = 0; temp <= n && i < n; i++) {
        if (temp == n) {
            return true;
        }
        temp *= 3;
    }
    return false;
}