title: Fake Coin Problem
body: <p>Classic problem with 12 coins ( or marbles) one of which is fake. Fake coin assumed to be lighter than real one.</p>
  
  <p>Having scales to compare coins (or marbles).</p>
  
  <p>One can do comparison one by one and compare all 12 coins. </p>
  
  <p>More efficiently one can do it using Decrease By Factor algorithm. Which is divide the coin stack by 2 and compare 2 stacks on the scales.</p>
  
  <p>Big O of the decrease by factor 2 is log2n.</p>
  
  <p>There is more efficient decrease by factor 3 (log3n) algorithm but I have not yet found it.</p>
  
  <p>If anyone explains it and why it is more efficient let me know.</p>