leetcode-326 3 的幂

/**
 * @param {number} n
 * @return {boolean}
 */
var isPowerOfThree = function (n) {
  if (n === 1) return true;
  let i = 3;
  while (i < n) {
    i *= 3;
  }
  return i === n;
};

function isPowerOfThree(n) {
  if (n <= 0) return false;
  // n=Math.pow(3,x)
  // x=log3(n)=loge(n)/loge(3)
  const logResult = Math.log10(n) / Math.log10(3);
  return Number.isInteger(logResult);
}

// logₐ(b) = logₓ(b) / logₓ(a)