12. (12 points) The figure below is a $6 \times 6$ grid. Fill in the blank cells with the numbers $1 \sim 6$ such that each row and each column contains the numbers $1 \sim 6$ exactly once. The grid is also divided into 6 regions by bold lines, and each region must contain the numbers $1 \sim 6$ exactly once. What is the four-digit number $\overline{\mathrm{ABCD}}$ formed by the first 4 numbers in the bottom row? $\qquad$
12. (12 points) As shown in the figure, it is a $6 \times 6$ grid. Fill in the numbers $1 \sim 6$ in the blank cells so that each row and each column contain the numbers $1 \sim 6$ exactly once. The grid is also divided into 6 regions by bold lines, and each region contains the numbers $1 \sim 6$ exactly once. What is the four-digit number $\overline{\mathrm{ABCD}}$ formed by the first 4 numbers in the bottom row? $\qquad$ .

【Solution】Solution: According to the problem, we know:
The 5 in the first row can only be placed in the 5th cell, which then leads to the 5 in the second row being in the first column, and the 5 in the fifth row being in the second column;

The 4 in the top-left block can only be placed in the 4th cell of the 2nd row.
So the 4 in the 6th row can only be in $B$.
The two cells in the third column above are 3 and 6, so the two cells below must be 1 and 2. $D$ is 3,
$A$ cannot be 1, so $C$ is 1, and thus, according to the last row, $A$ is 2.
Therefore, the answer is: 2413.