diff --git a/program4.c b/program4.c
new file mode 100644
index 0000000..0969562
--- /dev/null
+++ b/program4.c
@@ -0,0 +1,182 @@
+//#include <stdio.h>
+//#include <stdbool.h>
+//#include <stdlib.h>
+//#include <time.h>
+//
+//void printMatrix(int matrix[9][9]) {
+//    for (int i = 0; i < 9; i++) {
+//        if (i == 0 || i == 3 || i == 6) {
+//            printf("|-----------------------|\n");
+//        }
+//        for (int j = 0; j < 9; j++) {
+//            if (j == 0 || j == 3 || j == 6) {
+//                printf("| ");
+//            }
+//            if (matrix[i][j] == 0) {
+//                printf(". ");
+//            }
+//            else {
+//                printf("%d ", matrix[i][j]);
+//            }
+//            printf("|\n");
+//        }
+//        printf("|-----------------------|\n");
+//    }
+//}
+//
+//
+//bool usedInRow(int matrix[9][9], int row, int num) {
+//    for (int col = 0; col < 9; col++) {
+//        if (matrix[row][col] == num) {
+//            return true;
+//        }
+//    }
+//    return false;
+//}
+//bool usedInCol(int matrix[9][9], int col, int num) {
+//    for (int row = 0; row < 9; row++) {
+//        if (matrix[row][col] == num) {
+//            return true;
+//        }
+//    }
+//    return false;
+//}
+//
+//bool usedInBox(int matrix[9][9], int boxStartRow, int boxStartCol, int num) {
+//    for (int row = 0; row < 3; row++) {
+//        for (int col = 0; col < 3; col++) {
+//            if (matrix[row + boxStartRow][col + boxStartCol] == num) {
+//                return true;
+//            }
+//        }
+//    }
+//    return false;
+//}bool isSafe(int matrix[9][9], int row, int col, int num) {
+//    return!usedInRow(matrix, row, num) &&!usedInCol(matrix, col, num) &&!usedInBox(matrix, row - row % 3, col - col % 3, num);
+//}
+//bool findEmptyLocation(int matrix[9][9], int *row, int *col) {
+//    for (*row = 0; *row < 9; (*row)++) {
+//        for (*col = 0; *col < 9; (*col)++) {
+//            if (matrix[*row][*col] == 0) {
+//                return true;
+//            }
+//        }
+//    }
+//    return false;
+//}
+//
+//bool solveSudoku(int matrix[9][9]) {
+//    int row, col;
+//    if (!findEmptyLocation(matrix, &row, &col)) {
+//        return true; // 数独已解决
+//    }
+//    for (int num = 1; num <= 9; num++) {
+//        if (isSafe(matrix, row, col, num)) {
+//            matrix[row][col] = num;
+//            if (solveSudoku(matrix)) {
+//                return true;
+//            }
+//            matrix[row][col] = 0; // 回溯
+//        }
+//    }
+//    return false;
+//}
+//
+//bool checkRows(int matrix[9][9]) {
+//    for (int i = 0; i < 9; i++) {
+//        int count[9] = {0};
+//        for (int j = 0; j < 9; j++) {
+//            if (matrix[i][j] > 0 && matrix[i][j] <= 9) {
+//                int num = matrix[i][j] - 1;
+//                if (count[num] > 0) {
+//                    return false;
+//                }
+//                count[num]++;
+//            }
+//        }
+//    }
+//    return true;
+//}
+//
+//bool checkColumns(int matrix[9][9]) {
+//    for (int j = 0; j < 9; j++) {
+//        int count[9] = {0};
+//        for (int i = 0; i < 9; i++) {
+//            if (matrix[i][j] > 0 && matrix[i][j] <= 9) {
+//                int num = matrix[i][j] - 1;
+//                if (count[num] > 0) {
+//                    return false;
+//                }
+//                count[num]++;
+//            }
+//        }
+//    }
+//    return true;
+//}
+//
+//bool checkSubMatrices(int matrix[9][9]) {
+//    for (int row = 0; row < 9; row += 3) {
+//        for (int col = 0; col < 9; col += 3) {
+//            int count[9] = {0};
+//            for (int i = row; i < row + 3; i++) {
+//                for (int j = col; j < col + 3; j++) {
+//                    if (matrix[i][j] > 0 && matrix[i][j] <= 9) {
+//                        int num = matrix[i][j] - 1;
+//                        if (count[num] > 0) {
+//                            return false;
+//                        }
+//                        count[num]++;
+//                    }
+//                }
+//            }
+//        }
+//    }
+//    return true;
+//}
+//
+//bool isSudokuMatrix(int matrix[9][9]) {
+//    return checkRows(matrix) && checkColumns(matrix) && checkSubMatrices(matrix);
+//}
+//
+//int main() {
+//    printf("The original Sudoku matrix: \n");
+//    int matrix[9][9] = {
+//        {5, 3, 0, 0, 7, 0, 0, 0, 0},
+//        {6, 0, 0, 1, 9, 5, 0, 0, 0},
+//        {0, 9, 8, 0, 0, 0, 0, 6, 0},
+//        {8, 0, 0, 0, 6, 0, 0, 0, 3},
+//        {4, 0, 0, 8, 0, 3, 0, 0, 1},
+//        {7, 0, 0, 0, 2, 0, 0, 0, 6},
+//        {0, 6, 0, 0, 0, 0, 2, 8, 0},
+//        {0, 0, 0, 4, 1, 9, 0, 0, 5},
+//        {0, 0, 0, 0, 8, 0, 0, 7, 9}
+//    };
+//    printMatrix(matrix);
+//    bool valid = isSudokuMatrix(matrix);
+//    if (valid) {
+//        printf("True:Valid initial Sudoku matrix!\n");
+//        if (solveSudoku(matrix)) {
+//            printf("The solution of Sudoku matrix:\n");
+//            printMatrix(matrix);
+//        } else {
+//            printf("No solution!\n");
+//        }
+//    } else {
+//        printf("False:Invalid initial Sudoku matrix!\n");
+//        for (int j = 0; j < 9; j++) {
+//            int count[9] = {0};
+//            for (int i = 0; i < 9; i++) {
+//                if (matrix[i][j] > 0 && matrix[i][j] <= 9) {
+//                    int num = matrix[i][j] - 1;
+//                    if (count[num] > 0) {
+//                        printf("The number %d in the col %d has been used!\n", matrix[i][j], j);
+//                        break;
+//                    }
+//                    count[num]++;
+//                }
+//            }
+//        }
+//        printf("No solution!\n");
+//    }
+//    return 0;
+//}