AlgoDaily 07: Power of Three
“Given an integer num, write a method to determine if it is a power of 3.”
console.log(powerOfThree(9));
// true
To calculate a power of x, we could keep multiplying by x until we hit the exponent.
That means to see if something is a power of x, we can do the reverse and keep diving by x until we hit 1 or a number that is not a multiple of 3.
E.g. for 9, we’d go 9, 3, 1 and identify it as a power of 3. For 12, we’d go 12, 4 and identify it as not a power of 3.
This has O(log3(n)) complexity.
function powerOfThree(x) {
while (true) {
x /= 3;
if (x === 1) {
return true;
}
if (x % 3 !== 0) {
return false;
}
}
}
Test cases:
powerOfThree(9);
// true
powerOfThree(7);
// false
powerOfThree(729);
// true
powerOfThree(12);
// false
powerOfThree(15);
// false