Day 19 - LeetCode 342. Power of Four

LeetCode 342. Power of Four

題目

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.+

Example: Given num = 16, return true. Given num = 5, return false.
Follow up: Could you solve it without loops/recursion?

翻譯

判斷一個32bits的int整數是否為4的倍數。
進階：不用迴圈，遞迴解題。

想法

一直除4, 或用4進位

詳細參閱

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Code

/**
 * @param {number} num
 * @return {boolean}
 */
var isPowerOfFour = function(num) {

    if ( num <= 0 || num == 2 ) {
        return false;
    }
    if ( num === 1 ) {
        return true;
    }

    while ( num >= 4 && num % 4 === 0 ) {
        num = num / 4;
    }

    return num === 1;
};

/**
 * @param {number} num
 * @return {boolean}
 */
var isPowerOfFour = function(num) {
    
    if ( num <= 0 ) {
        return false;
    }

    return /^10*$/.test(num.toString(4));
};

Run