diff --git a/t4.cpp b/t4.cpp
new file mode 100644
index 0000000..e6d5b4f
--- /dev/null
+++ b/t4.cpp
@@ -0,0 +1,189 @@
+#include <stdio.h>
+int f[9] = {0}, copy[9][9] = {0};
+int t1[9][9] = {0}, t2[9][9] = {0}, t3[9][9] = {0};
+// 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}};
+// int board[9][9] = {{8, 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}};
+int board[9][9] = {{5, 2, 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}};
+int ifans = 0;
+void f1()
+{
+    printf("|");
+    for (int i = 0; i < 23; i++)
+    {
+        printf("-");
+    }
+    printf("|\n");
+}
+void operate()
+{
+    for (int i = 0; i < 9; i++)
+    {
+        if (i % 3 == 0)
+        {
+            f1();
+        }
+        printf("| ");
+        for (int j = 0; j < 9; j++)
+        {
+            if (j % 3 == 0 && j)
+            {
+                printf("| ");
+            }
+            printf("%d ", board[i][j]);
+        }
+        printf("|\n");
+    }
+    f1();
+}
+int judge()
+{
+    for (int i = 0; i < 9; i++)
+    {
+        for(int j = 0; j < 9; j++)
+        {
+            if (board[i][j])
+            {
+                t1[i][board[i][j] - 1]++;
+                t2[j][board[i][j] - 1]++;
+                t3[(i / 3) * 3 + j / 3][board[i][j] - 1]++;
+            }
+        }
+    }
+    for (int i = 0; i < 9; i++)
+    {
+        for (int num = 0; num < 9; num++)
+        {
+            if (t1[i][num] > 1)
+            {
+                printf("False:Invalid initial Sudoku matrix!\n");
+                printf("      The number %d in the row %d has been used!\n", num + 1, i + 1);
+                printf("No solution!");
+                return 0;
+            }
+            else if (t2[i][num] > 1)
+            {
+                printf("False:Invalid initial Sudoku matrix!\n");
+                printf("      The number %d in the col %d has been used!\n", num + 1, i + 1);
+                printf("No solution!");
+                return 0;
+            }
+            else if (t3[i][num] > 1)
+            {
+                printf("False:Invalid initial Sudoku matrix!\n");
+                printf("      The number %d in the block %d has been used!\n", num + 1, i + 1);
+                printf("No solution!");
+                return 0;
+            }
+        }
+    }
+    printf("True:Valid initial Sudoku matrix!\n");
+    return 1;
+}
+void fill(int x, int y)
+{
+    int num;
+    if (x == 9 && y == 0)
+    {
+        printf("The solution of Sudoku matrix:\n");
+        operate();
+        ifans = 1;
+    }
+    else
+    {
+        if (copy[x][y])
+        {
+            if (y == 8)
+            {
+                fill(x + 1, 0);
+                if (x == 0 && y == 0 && ifans == 0)
+                {
+                    printf("No solution!");
+                }
+                return;
+            }
+            else{
+                fill(x, y + 1);
+                if (x == 0 && y == 0 && ifans == 0)
+                {
+                    printf("No solution!");
+                }
+                return;
+            }
+        }
+        else
+        {
+            for(num = 1; num <= 9; num++)
+            {
+                if (t1[x][num - 1] == 0 && t2[y][num - 1] == 0 && t3[(x / 3) * 3 + y / 3][num - 1] == 0)
+                {
+                    board[x][y] = num;
+                    t1[x][num - 1] = 1;
+                    t2[y][num - 1] = 1;
+                    t3[(x / 3) * 3 + y / 3][num - 1] = 1;
+                    if (y == 8)
+                    {
+                        // operate();
+                        fill(x + 1, 0);
+                        board[x][y] = 0;
+                        t1[x][num - 1] = 0;
+                        t2[y][num - 1] = 0;
+                        t3[(x / 3) * 3 + y / 3][num - 1] = 0;
+                    }
+                    else{
+                        // operate();
+                        fill(x, y + 1);
+                        board[x][y] = 0;
+                        t1[x][num - 1] = 0;
+                        t2[y][num - 1] = 0;
+                        t3[(x / 3) * 3 + y / 3][num - 1] = 0;
+                    }
+                }
+            }
+            if (x == 0 && y == 0 && ifans == 0)
+            {
+                printf("No solution!");
+            }
+            return;
+        }
+    }
+}
+int main()
+{
+    printf("The original Sudoku matrix:\n");
+    operate();
+    for (int i = 0; i < 9; i++)
+    {
+        for (int j = 0; j < 9; j++)
+        {
+            copy[i][j] = board[i][j];
+        }
+    }
+    if(judge())
+    {
+        fill(0,0);
+    }
+}
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