title: Longest string with 3 characters without adjacent repeating secuences?
body: <p>I tried making a tree but cannot make it in time.</p>
  
  <p>The longest I have found is 15: 
  BCACBABCABACBABC</p>
  
  <p>For example (wrong):
  ababcabcab</p>
  
  <p>(abcabc repeats abc. Obviously abcabc is not the only wrong thing)</p>
  
  <p>Another:
  aa</p>
  
  <p>(a repeats)</p>
  
  <p>This is a correct example (it is not wrong):
  ABA </p>