342 Power of Four
Problem Statement
Given an integer n, return true if it is a power of four. Otherwise, return false.
An integer n is a power of four, if there exists an integer x such that n == 4x.
Input: n = 16
Output: true
Input: n = 5
Output: false
Input: n = 1
Output: true
Approach
We can solve this with Recursion where we recursively call the function with n = n / 4.
The base case has to be defined as n === 1. If we reach 1 we know that the passed in number is a power of four.
To get to the base case we have to understand exponents. If the integer n is equal to 1 it can be expressed as 4^0, which satisfies the definition of a power of four and is the smallest possible case of power of four.
Solution
var isPowerOfFour = function(n) {
if (n === 1) return true
if (n < 1) return false
return isPowerOfFour(n / 4)
};