# Sudoku Puzzle
Solve this 4×4 Sudoku puzzle. Each row, column, and 2×2 box must contain the digits 1 through 4 exactly once.
```
+---+---+---+---+
| . | . | 3 | . |
+---+---+---+---+
| 2 | . | . | . |
+---+---+---+---+
| . | 1 | . | . |
+---+---+---+---+
| . | . | . | 4 |
+---+---+---+---+
```
Find values for all empty cells that satisfy the Sudoku constraints.