The code copy is as follows:
import java.util.Calendar;
import java.util.Date;
public class Matrix {
private int matrix[][];
private long timeAfter=0;
private long timeBefore =0;
public Matrix(int m[][]) {
matrix = new int[9][9];
for (int i=0; i<9; i++)
for(int j= 0; j<9; j++)
matrix[i][j]=m[i][j];
this.timeBefore = Calendar.getInstance().getTimeInMillis();
}
public void backTrack(int i, int j)
{
//Recycle system memory resources
System.gc();
if( i==8 && j>=9 )
{
this.timeAfter = Calendar.getInstance().getTimeInMillis();
//Successful output matrix
this.showMatrix();
return;
}
if(j == 9) {j = 0; i++;}
if(matrix[i][j] == 0)
{
//The number is zero
for(int k=1; k<=9; k++)
{
if(bound(i,j,k))
{
matrix[i][j] = k ;
//Meet the conditions, find the next square
backTrack(i,j+1);
matrix[i][j] = 0;
}
}
}else
{
//The number is not zero, just look for the next one
backTrack(i, j+1);
}
}
/**
* Determine whether the number to be filled in is duplicated with the same column and the numbers in the same nine grid
*/
private boolean bound(int i, int j, int k) {
int m = i/3;
int n = j/3;
for(int p = 0; p<9; p++)
{
if(k == matrix[i][p])
{
return false;
}
if(k == matrix[p][j])
{
return false;
}
if(k == matrix[3*m+p/3][3*n+p%3])
{
return false;
}
}
return true;
}
/**
* Print the problem solving time
* @return
*/
public long printTime()
{
return this.timeAfter-this.timeBefore;
}
/**
* Print matrix
*/
public void showMatrix()
{
for(int i=0; i<9; i++)
{
for(int j=0; j<9; j++)
{
System.out.print(matrix[i][j]+" ");
}
System.out.println ();
}
System.out.println ();
System.out.println("Problem solving time: "+printTime()+"ms");
System.out.println ();
}
public static void main(String[] args) {
int matrix[][] = {
{3,0,6,0,5,7,0,0,0},
{7,9,0,0,2,4,0,0,0},
{0,5,0,6,0,0,9,7,4},
{8,0,1,0,0,9,0,0,0},
{0,2,0,3,0,8,0,0,7},
{4,0,0,0,6,0,5,0,0},
{0,0,4,0,3,6,0,5,0},
{2,0,3,7,0,5,0,0,1},
{0,0,7,4,1,0,6,0,0}};
int ma1[][]={
{0,3,0,0,0,5,0,6,0},
{0,1,0,0,0,3,0,8,0},
{0,4,0,0,0,0,0,0,0,0,7},
{0,0,7,0,2,4,0,0,0},
{5,0,0,0,9,0,0,0,0,0},
{0,8,0,3,0,0,5,0,0},
{0,0,0,8,0,0,0,0,0,0},
{0,0,9,0,0,0,0,0,7,3},
{0,5,0,9,0,0,0,0,0,2}};
int ma2[][]={
{0,0,0,0,8,4,0,0,0},//8
{0,0,0,2,0,3,0,8,0},
{8,3,0,9,0,0,0,5,0},
{0,5,3,0,9,0,7,0,0},
{0,0,0,6,3,7,0,4,5},//7
{0,7,0,5,0,0,0,0,0,0},
{0,0,6,8,0,0,0,0,0,0},
{3,0,0,0,2,9,0,0,0},
{2,0,9,3,0,0,0,0,1}};//3
// It is known as the most difficult sudoku in the world
int[][] sudoku = {
{ 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 0, 3, 6, 0, 0, 0, 0, 0, 0, 0 },
{ 0, 7, 0, 0, 9, 0, 2, 0, 0 },
{ 0, 5, 0, 0, 0, 0, 7, 0, 0, 0 },
{ 0, 0, 0, 0, 4, 5, 7, 0, 0 },
{ 0, 0, 0, 1, 0, 6, 0, 3, 0 },
{ 0, 0, 1, 0, 0, 0, 0, 6, 8 },
{ 0, 0, 8, 5, 0, 0, 0, 1, 0 },
{ 0, 9, 0, 0, 0, 0, 4, 0, 0 }};
Matrix m = new Matrix(sudoku);
m.backTrack(0, 0);
}
}