diff --git a/sy4(2).c b/sy4(2).c
new file mode 100644
index 0000000..5359cdd
--- /dev/null
+++ b/sy4(2).c
@@ -0,0 +1,121 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+#define SIZE 9
+
+// 函数声明
+bool isSafe(int grid[SIZE][SIZE], int row, int col, int num);
+bool solveSudoku(int grid[SIZE][SIZE]);
+void findInvalidReason(int grid[SIZE][SIZE]);
+void print(int matrix[SIZE][SIZE]);
+
+// 主函数
+int main() {
+    int sudoku[SIZE][SIZE] = {  {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}};
+
+    printf("The original Sudoku matrix: \n");
+    print(sudoku);
+
+    if (solveSudoku(sudoku)) {
+        printf("True:Valid initial Sudoku matrix!\n");
+        printf("The solution of Sudoku matrix:\n");
+        print(sudoku);
+    } else {
+        printf("False:Invalid initial Sudoku matrix!\n");
+        findInvalidReason(sudoku);
+        printf("No solution!\n");
+    }
+
+    return 0;
+}
+
+
+
+// 检查在给定的数独矩阵中，数字 num 能否放在位置 (row, col)
+bool isSafe(int grid[SIZE][SIZE], int row, int col, int num) {
+    int x, i, j;
+    // 检查行
+    for (x = 0; x < SIZE; x++)
+        if (grid[row][x] == num)
+            return false;
+
+    // 检查列
+    for (x = 0; x < SIZE; x++)
+        if (grid[x][col] == num)
+            return false;
+
+    // 检查 3x3 宫格
+    int startRow = row - row % 3, startCol = col - col % 3;
+    for (i = 0; i < 3; i++)
+        for (j = 0; j < 3; j++)
+            if (grid[i + startRow][j + startCol] == num)
+                return false;
+
+    return true;
+}
+
+// 解决数独问题的递归函数
+bool solveSudoku(int grid[SIZE][SIZE]) {
+    int row, col, num;
+    // 查找空白格
+    for (row = 0; row < SIZE; row++)
+        for (col = 0; col < SIZE; col++)
+            if (grid[row][col] == 0) {
+                for (num = 1; num <= 9; num++) {
+                    if (isSafe(grid, row, col, num)) {
+                        grid[row][col] = num;
+                        if (solveSudoku(grid))
+                            return true;
+                        grid[row][col] = 0; // 回溯
+                    }
+                }
+                return false; // 触发回溯
+            }
+    return true; // 解决了数独
+}
+
+// 查找不满足数独定义的原因
+void findInvalidReason(int grid[SIZE][SIZE]) {
+    int row, col, num, blockRow, blockCol;
+    for (row = 0; row < SIZE; row++) {
+        for (col = 0; col < SIZE; col++) {
+            if (grid[row][col] != 0) {
+                for (num = 1; num <= 9; num++) {
+                    if (grid[row][col] == num && !isSafe(grid, row, col, num)) {
+                        blockRow = row - row % 3;
+                        blockCol = col - col % 3;
+                        printf("The number %d is duplicated in row %d, column %d, or block %d.\n", num, row + 1, col + 1, (blockRow / 3) * 3 + (blockCol / 3) + 1);
+                        return;
+                    }
+                }
+            }
+        }
+    }
+}
+
+// 格式化输出数独矩阵
+void print(int matrix[SIZE][SIZE]) {
+    int i, j;
+    printf("|-----------------------------|\n");
+    for (i = 0; i < SIZE; i++) {
+        printf("|");
+        for (j = 0; j < SIZE; j++) {
+            printf("%2d ", matrix[i][j]);
+            if ((j + 1) % 3 == 0 ) printf("|");
+        }
+        printf("\n");
+        if ((i + 1) % 3 == 0 && i < SIZE-1) {
+            printf("|-----------------------------|\n");
+        }        
+    }
+    printf("|-----------------------------|\n");
+
+}