Color Master Sudoku

4x4 Sudoku is a simplified version of traditional Sudoku. The rules are similar to those of standard Sudoku, except that the board is smaller.
The specific rules are as follows:
1. Board structure: The Sudoku board is a 4x4 grid divided into four 2x2 small grid areas.
2. Number range: Each space on the board needs to be filled with hearts, clubs, diamonds, and spades.
3. Number filling rules:
1. The elements in each row (horizontally) must be hearts, clubs, diamonds, and blacks and cannot be repeated.
2. The elements in each column (vertically) must be hearts, clubs, diamonds, and blacks and cannot be repeated.
3. The elements in each 2x2 small grid area must be hearts, clubs, diamonds, and blacks and cannot be repeated.
4. Goal: Based on the given elements (usually there are some pre-filled grids), fill in the remaining spaces through logical reasoning so that the entire board meets the above rules.
This 4x4 Sudoku is usually suitable for beginners because it is simpler than the traditional 9x9 Sudoku. However, it still requires careful reasoning to solve!