2. Balance {1,2,3,4} and {5,6,7,8}. If balanced: step 3, else: step 6.

3. It means one of {9, 10, 11} is different. Balance 9, 10. If balanced: step 4, else: step 5.

4. It means 11 is different. Just balance it with any one, and you'll know whether it's lighter or heavier.

5. Either 9 or 10 is different, balance 9 with 11; if balanced, 10 is different, otherwise 9 is different. Based on step 3, you know whether the different one is heavier or lighter.

6. The different one is in either {1,2,3,4} or {5,6,7,8}. Let's assume {1,2,3,4} is heavier than {5,6,7,8}. Remove 1 (potentially heavier), and 5,6 (potentially lighter), switch 2 and 7, then add 9 into the second group. Now we have {3,4,7} and {2,8,9}. Balance them again. If balanced: step 7, else step 8.

7. It means either 1 is heavier or one of {5,6} is lighter. Balance 5 and 6. If balanced, 1 is heavier, otherwise, whichever lighter is the one.

8. If {3,4,7} > {2,8,9}, it means that either one of {3,4} is heavier, or 8 is lighter. Balance 3 and 4. If balanced, 8 is lighter, otherwise whichever heavier is the one. If {3,4,7} < {2,8,9}, it means that either 7 is lighter or 2 is heavier. Balance 7 with 3 (or any regular one). If balanced, 2 is heavier, otherwise 7 is lighter.