diff --git a/4.cpp b/4.cpp
new file mode 100644
index 0000000..fbdd709
--- /dev/null
+++ b/4.cpp
@@ -0,0 +1,113 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+void format(int board[9][9]) { 
+    for (int i = 0; i < 9; i++) {
+        for (int j = 0; j < 9; j++) {
+            printf("%d ", board[i][j]);
+            if ((j + 1) % 3 == 0 && j != 8) {
+                printf("| ");
+            }
+        }
+        if ((i + 1) % 3 == 0 && i != 8) {
+            printf("\n---------------------\n");
+        }
+        else { printf("\n"); }
+    }
+}
+
+bool panduan(int board[9][9]) {
+    
+    for (int i = 0; i < 9; i++) {
+        bool row[10] = { 0 }, col[10] = { 0 }, block[10] = { 0 }; 
+        for (int j = 0; j < 9; j++) {
+           
+            if (board[i][j] != 0) {
+                if (row[board[i][j]]) {
+                    printf("The number %d in row %d has been used!\n", board[i][j], i);
+                    return false;
+                }
+                row[board[i][j]] = true;
+            }
+            
+            if (board[j][i] != 0) {
+                if (col[board[j][i]]) {
+                    printf("The number %d in column %d has been used!\n", board[j][i], i);
+                    return false;
+                }
+                col[board[j][i]] = true;
+            }
+           
+            int blockRow = 3 * (i / 3), blockCol = 3 * (i % 3);
+            if (board[blockRow + j / 3][blockCol + j % 3] != 0) {
+                if (block[board[blockRow + j / 3][blockCol + j % 3]]) {
+                    printf("The number %d in block %d has been used!\n",
+                        board[blockRow + j / 3][blockCol + j % 3], (i / 3) * 3 + (i % 3));
+                    return false;
+                }
+                block[board[blockRow + j / 3][blockCol + j % 3]] = true;
+            }
+        }
+    }
+    return true;
+}
+
+
+bool jie(int board[9][9]) {
+    for (int row = 0; row < 9; row++) {
+        for (int col = 0; col < 9; col++) {
+            if (board[row][col] == 0) { 
+                for (int num = 1; num <= 9; num++) {
+                    board[row][col] = num; 
+                    if (panduan(board)) { 
+                        if (panduan(board)) {
+                            return true;
+                        }
+                    }
+                    board[row][col] = 0; 
+                }
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
+int main()
+{
+    int board[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}};
+    void format(int board[9][9]);
+
+    printf("The original Sudoku matrix:\n");
+    format(board);
+
+    if (panduan(board)) {
+        printf("True: Valid initial Sudoku matrix!\n");
+        if (jie(board)) {
+            printf("The solution of Sudoku matrix:\n");
+            format(board);
+        }
+        else {
+            printf("No solution!\n");
+        }
+    }
+    else {
+        printf("False: Invalid initial Sudoku matrix!\n");
+        printf("No solution!\n");
+    }
+
+    return 0;
+
+
+
+}
+
+