Here is game played by little guys. There is a 4 * 4 square, and the square is filled with the characters 'A', 'B', 'C' and 'D'. Each kind of character appears exactly 4 times. You can arbitrarily swap two adjacent characters (horizontal or vertical). At the beginning of the game you should choose a character (from 'A', 'B', 'C' and 'D') as you target character, when any 2 * 2 sub-square contains the same character as the character you have chosen before, you win the game.
These little guys want to use minimal times of swap to win the game. Now they turn to you. Can you help them?