Erich's Holiday Puzzles

Go in with 2011, and go out with 2012. You may pass through an operation several times, but not twice in a row.

2011 2012

  Please share the answer.

Tip of the day :  A Sudoku Puzzle Needs at least 17 Clues. 

Gary McGuire: I know you have posted and written about Sudoku. You might have some interest in the minimum number of clues problem, so I write to let you know that we have completed the exhaustive search for a 16-clue Sudoku puzzle, and the result is that none exists. Therefore we have solved the problem, and 17 is the answer! There is no 16-Clue Sudoku.