Problem

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

Example 1:

Input: 16 Output: true

Example 2:

Input: 5 Output: false

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

Pre analysis

Will use the power of log . Also log 16 (base e) / log 4 (base e) = log 16(base 4)

Another solution

Recursive division

var isPowerOfFour = function(num) {
    if (num < 1) {return false;}
    while (num > 1) {
        if (num % 4 === 0) {
            num = num/4;
        }
        else {
            return false;
        }
    }
    return true;
};

Greedy solution

var isPowerOfFour = function(num) {
    count = 0

    while(Math.pow(4, count) < num)
        {
        count += 1;
        }

    return (Math.pow(4, count) == num);
};