One Pager Cheat Sheet

• Write a method powerOfThree which determines if a given non zero positive integer num between 1 and 2147483647 is a power of 3, with an expected space complexity of O(logn) and an expected time complexity of O(1).
• The ^6 in 3^6 stands for the exponent calculated using the formula base^exponent = result.
• Loops are a useful control structure in programming used to repeat certain code multiple times, saving the developer time when dealing with large data sets or unknown iterations.
• The while-loop can be considered as a repeating IF-statement because it needs an initial evaluation of the condition before continuing to repeat a certain set of instructions as long as the condition is true.
• The number 729 can be expressed using exponential notation as 3^6, since it is the result of raising 3 to the 6th power.
• The exponential value of any number can be calculated without loops, simply by raising that number to the power of itself.
• We can solve this problem in O(logn) time complexity and O(1) space complexity by continuously dividing the number by 3.

This is our final solution.

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}

var assert = require('assert');

​

function powerOfThree(num) {

  let currentQuotient = num;

  if (currentQuotient === 1) {

    return true;

  }

  while (currentQuotient > 0) {

    currentQuotient = currentQuotient / 3;

    if (currentQuotient === 1) {

      return true;

    }

  }

  return false;

}

​

console.log(powerOfThree(9));

console.log(powerOfThree(7));

​

try {

  assert.equal(powerOfThree(9), true);

​

  console.log('PASSED: ' + 'powerOfThree(9) should be true');

} catch (err) {

  console.log(err);

}

​

try {

  assert.equal(powerOfThree(7), false);

​

  console.log('PASSED: ' + 'powerOfThree(7) should be false');

} catch (err) {

Alright, well done! Try another walk-through.

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