diff --git a/4 b/4
new file mode 100644
index 0000000..9fd8ac8
--- /dev/null
+++ b/4
@@ -0,0 +1,196 @@
+#include <stdio.h>
+#include <ctype.h>
+void output(const int (*p_board)[9]);
+int check(const int (*p_board)[9], int row, int column, int n);
+int solve(int (*p_board)[9]);
+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}};
+	printf("The original Sudoku matrix:\n");
+	output(board);
+    int state;
+    	int i,j,k;
+	int f=1;
+	for(i=0;i<9;i++)
+	{
+		int x[10]={0};
+		for(j=0;j<9;j++)
+		{
+			x[board[i][j]]+=1;
+		}
+		for(k=1;k<=9;k++)
+		{
+			if(x[k]>1&&f==1)
+			{
+			printf("False:Invalid initial Sudoku matrix!\n");
+			printf("The number %d in the col %d has been used!\n",k,i+1);
+			f=0;
+			}
+		}
+	}
+	for(i=0;i<9;i++)
+	{
+		int z[10]={0};
+		for(j=0;j<9;j++)
+		{
+			z[board[j/3+(i%3)*3][j%3+(i/3)*3]]+=1;
+		}
+		for(k=1;k<=9;k++)
+		{
+			if(z[k]>1&&f==1)
+			{
+				printf("False:Invalid initial Sudoku matrix!\n");
+				printf("The number %d in the block %d has been used!\n",k,i+1);
+				f=0;
+			}
+		}
+	}
+	for(i=0;i<9;i++)
+	{
+		int y[10]={0};
+		for(j=0;j<9;j++)
+		{
+			y[board[j][i]]+=1;
+		}
+		for(k=1;k<=9;k++)
+		{
+			if(y[k]>1&&f==1)
+			{
+				printf("False:Invalid initial Sudoku matrix!\n");
+				printf("The number %d in the row %d has been used!\n",k,i+1);
+				f=0;
+			}
+		}
+	}
+	if(f==1)printf("True:Valid initial Sudoku matrix!\n");
+    state=solve(board);
+    if (state)
+    {
+        printf("The solution of Sudoku matrix:\n");
+        output(board);
+    }
+    else
+    {
+        printf("No solution!\n");
+    }
+    return 0;
+}
+
+void output(const int (*p_board)[9])
+{
+    for (int i=0;i<9;i++)
+    {
+		if (i%3==0)
+		{
+			printf("|-----------|\n");
+		}	
+        for (int j=0;j<9;j++)
+        {
+			if (j%3==0)
+			{
+				printf("|");
+			}
+			printf("%d", p_board[i][j]);
+        }
+        printf("|\n");
+    }
+    printf("|-----------|\n");
+}
+int check(const int (*p_board)[9], int row, int column, int num)
+{
+    int i, j, center_row, center_column;
+    for (j = 0; j < 9; j++)
+    {
+        if (p_board[row][j] == num)
+        {
+            return 0;
+        }
+    }
+    for (i=0;i<9;i++) 
+    {
+        if (p_board[i][column]==num)
+        {
+            return 0;
+        }
+    }
+    center_row=row/3*3;                      
+    center_column =column/3*3;
+    for (i=center_row;i<=center_row+2;i++)
+    {
+        for (j=center_column;j<=center_column+2;j++)
+        {
+            if (p_board[i][j]==num)
+            {
+                return 0;
+            }
+        }
+    }
+    return 1;
+}
+int solve(int (*p_board)[9])
+{
+    struct Idex
+    {
+        int row;
+        int column;
+        int state; 
+    };
+    struct Idex arr_idex[81]; 
+    int i,j;
+    int end=-1, now=0;  
+    for (i=0;i<9;i++) 
+    {
+        for (j=0;j<9;j++)
+        {
+            if (p_board[i][j]==0)
+            {
+                end++;
+                arr_idex[end].row=i;
+                arr_idex[end].column=j;
+                arr_idex[end].state=1;
+            }
+        }
+    }
+    for (now=0;now<=end;)
+    {
+        if (arr_idex[now].state > 9)
+        {
+            if (now==0)
+            {
+                return 0;
+            }
+            else
+            {
+                arr_idex[now].state=1;
+                p_board[arr_idex[now].row][arr_idex[now].column]=0;
+                now--;
+                continue;
+            }
+        }
+        for (i=arr_idex[now].state;i<=9;i++) 
+        {
+            if (check(p_board,arr_idex[now].row,arr_idex[now].column,i)) 
+            {
+                arr_idex[now].state=i+1; 
+                p_board[arr_idex[now].row][arr_idex[now].column]=i;
+                now++;
+                break;
+            }
+            else if (i == 9)
+            {
+                arr_idex[now].state=1; 
+                p_board[arr_idex[now].row][arr_idex[now].column]=0;
+                now--;
+            }
+        }
+    }
+    return 1;
+}
\ No newline at end of file