diff --git a/T4.cpp b/T4.cpp
new file mode 100644
index 0000000..59df12e
--- /dev/null
+++ b/T4.cpp
@@ -0,0 +1,125 @@
+#include <stdio.h>
+#include <stdbool.h>
+void print_sudoku(int matrix[9][9]) {
+    int i,j;
+    for (i = 0; i < 9; i++) {
+        for (j = 0; j < 9; j++) {
+            if (matrix[i][j] == 0) {
+                printf(". ");
+            } else {
+                printf("%d ", matrix[i][j]);
+            }
+        }
+        printf("\n");
+    }
+}
+bool is_safe(int matrix[9][9], int row, int col, int num) {
+    int i,j;
+    for (i = 0; i < 9; i++) {
+        if (matrix[row][i] == num) {
+            return false;
+        }
+    }
+    for (i = 0; i < 9; i++) {
+        if (matrix[i][col] == num) {
+            return false;
+        }
+    }
+    int start_row = row - row % 3;
+    int start_col = col - col % 3;
+    for (i = 0; i < 3; i++) {
+        for (j = 0; j < 3; j++) {
+            if (matrix[i + start_row][j + start_col] == num) {
+                return false;
+            }
+        }
+    }
+
+    return true;
+}
+bool solve_sudoku(int matrix[9][9]) {
+    int i,j,num;
+    for (i = 0; i < 9; i++) {
+        for (j = 0; j < 9; j++) {
+            if (matrix[i][j] == 0) {
+                for (num = 1; num <= 9; num++) {
+                    if (is_safe(matrix, i, j, num)) {
+                        matrix[i][j] = num;
+                        if (solve_sudoku(matrix)) {
+                            return true;
+                        }
+                        matrix[i][j] = 0;
+                    }
+                }
+                return false; 
+            }
+        }
+    }
+    return true;
+}
+bool is_valid_sudoku(int matrix[9][9], char* error_message) {
+    int i,j;
+    for (i = 0; i < 9; i++) {
+        bool row_set[10] = {0}; 
+        bool col_set[10] = {0}; 
+        bool block_set[10] = {0}; 
+
+        for (j = 0; j < 9; j++) {
+            if (matrix[i][j] != 0 && row_set[matrix[i][j]]) {
+                sprintf(error_message, "Row %d has duplicates.", i + 1);
+                return false;
+            }
+            if (matrix[i][j] != 0) row_set[matrix[i][j]] = true;
+            if (matrix[j][i] != 0 && col_set[matrix[j][i]]) {
+                sprintf(error_message, "Column %d has duplicates.", i + 1);
+                return false;
+            }
+            if (matrix[j][i] != 0) col_set[matrix[j][i]] = true;
+            int block_row = (i / 3) * 3;
+            int block_col = (i % 3) * 3;
+            int num = matrix[block_row + j / 3][block_col + j % 3];
+            if (num != 0 && block_set[num]) {
+                sprintf(error_message, "Block starting at (%d,%d) has duplicates.", block_row + 1, block_col + 1);
+                return false;
+            }
+            if (num != 0) block_set[num] = true;
+        }
+    }
+    return true;
+}
+
+int main() {
+    int sudoku[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}
+    };
+
+    printf("The original Sudoku matrix:\n");
+    print_sudoku(sudoku);
+
+    char error_message[100];
+    bool valid = is_valid_sudoku(sudoku, error_message);
+
+    if (valid) {
+        printf("True: Valid initial Sudoku matrix!\n");
+        if (solve_sudoku(sudoku)) {
+            printf("The solution of Sudoku matrix:\n");
+            print_sudoku(sudoku);
+        } else {
+            printf("No solution!\n");
+        }
+    } else {
+        printf("False: Invalid initial Sudoku matrix!\n");
+        printf("%s\n", error_message);
+        printf("No solution!\n");
+    }
+
+    return 0;
+}