I'm sort of new to Java. Here is my stab at trying to make a Sudoku solver. As of right now this doesn't have a GUI, to enter the problem you have to modify the code itself. Usually the the program completes the Sudoku in around 30 milliseconds (starting with some filled values) and around 100 milliseconds if it has to start from scratch (starting with a blank sudoku). The problem I faced was that sometimes the programs keeps running without providing a solution, I have to manually stop it. Is that because the sudoku has only 1 or few solutions? or is it because it gets stuck it some kind of loop. What I also notice is that if the far bottom far right (8,8) is filled in the program doesn't even try to solve the sudoku. Perhaps because of the way my code is written it thinks that the sudoku is already solved. Could I instead have it check for the last unfilled spot instead of a fixed position?
package sudoku;
public class Sudoku {
static int userGrid[][]=new int[][]
{{0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0},
{0,0,0,0,0,0,0,0,0}};//[Horizontal][Vertical]
static int grid[][]=new int[9][9];//Program experiments
public static void main(String[] args) {
for(int i=0;i<9;i+=1) {
for (int j=0;j<9;j+=1) {
grid[i][j]=userGrid[i][j];
}
}
print(grid);
double timeStart=System.currentTimeMillis();
print(loop(0, 0, grid));
double timeEnd=System.currentTimeMillis();
System.out.println("That took "+(timeEnd - timeStart)+" milliseconds to complete");
}
public static int[][] loop(int y, int x, int[][] grid) {
while(!validity(8, 8, grid) || grid[8][8]==0)//while it's not solved
{
if(userGrid[y][x]!=0){
int yy,xx;
if (x==8) {yy=y+1;xx=0;} else {yy=y; xx=x+1;}
loop(yy, xx, grid);
} else {
if(grid[y][x]<9) {//going forward
grid[y][x]+=1;
if(validity(y, x, grid)) {
int yy,xx;
if (x==8) {yy=y+1;xx=0;} else {yy=y; xx=x+1;}
loop(yy, xx, grid);
}
} else {
grid[y][x]=0;
break;}
}
}
return grid;
}
public static boolean validity(int x, int y, int[][] grid) {
String temp="";
for(int i=0;i<9;i+=1) {
temp+=Integer.toString (grid[i][y]);//horizontal
temp+=Integer.toString (grid[x][i]);//vertical
temp+=Integer.toString (grid[(x/3)*3+i/3][(y/3)*3+i%3]);//square
}
int count=0, idx=0;
while((idx=temp.indexOf(Integer.toString (grid[x][y]),idx))!=-1)
{idx+=1;count+=1;}
return count==3;
}
public static void print(int[][] grid) {
System.out.println();
for(int i=0;i<9;i+=1) {
for (int j=0;j<9;j+=1) {
System.out.print(grid[i][j]);
}
System.out.println();
}
}
}
EDIT: I debugged the code and found the problems
The glitch was solved by looking for the last unfilled number instead of the bottom rightmost number (8,8)
Another problem I was experiencing was that it would not backtrack behind the preexisting numbers and would get stuck in an infinite loop. That was why it was running endlessly.
FIXED code:
package sudoku;
public class Sudoku {
static int userGrid[][]=new int[][]
{{2,0,0,4,0,0,0,0,0},
{0,0,4,0,9,0,0,0,0},
{0,0,0,0,6,0,8,7,0},
{7,0,2,0,0,0,0,8,0},
{0,0,0,7,0,0,0,0,9},
{0,4,9,0,0,2,0,0,5},
{0,8,0,0,0,7,1,9,3},
{0,5,0,0,0,4,0,0,0},
{0,0,0,8,0,0,0,0,0}};//[Horizontal][Vertical]
static int grid[][]=new int[9][9];//Program experiments
//static String pGrid[][]=new String[9][9];//Possibilities
public static void main(String[] args) {
for(int i=0;i<9;i+=1) {
for (int j=0;j<9;j+=1) {
grid[i][j]=userGrid[i][j];
}
}
print(grid);
double timeStart=System.currentTimeMillis();
int lastPos = findLastCell();
if (lastPos == 0){
return;
}
int lastY = lastPos % 16;
int lastX = lastPos / 16;
print(loop(0, 0, lastY, lastX, grid));
double timeEnd=System.currentTimeMillis();
System.out.println("That took "+(timeEnd - timeStart)+" milliseconds to complete");
}
public static int findLastCell(){
for (int i=8; i>=0; i--){
for (int j=8; j>=0; j--){
if (userGrid[i][j]==0){
return ((j * 16) + i);
}
}
}
return 0;
}
public static int[][] loop(int y, int x, int lastY, int lastX, int[][] grid) {
while(!validity(lastY, lastX, grid) || grid[lastY][lastX]==0)//while it's not solved
{
while (userGrid[y][x]!=0){
if (x==8)
{
// System.out.println("Here 2");
y=y+1;
x=0;
}
else
{
x=x+1;
}
}
if(grid[y][x]<9) {//going forward
grid[y][x]+=1;
if(validity(y, x, grid)) {
int yy,xx;
if (x==8)
{
//System.out.println("Here");
yy=y+1;
xx=0;
}
else
{
yy=y;
xx=x+1;
}
loop(yy, xx, lastY, lastX, grid);
}
} else {
grid[y][x]=0;
break;}
}
return grid;
}
public static boolean validity(int x, int y, int[][] grid) {
String temp="";
for(int i=0;i<9;i+=1) {
temp+=Integer.toString (grid[i][y]);//horizontal
temp+=Integer.toString (grid[x][i]);//vertical
}
for (int i=0; i<3; i++){
for (int j=0; j<3; j++){
temp+=Integer.toString (grid[(x/3)*3+i][(y/3)*3+j]);
//square (Java doesn't round the divided no.s if they
//are fractions. It jjust outputs them as 0
}
}
int count=0, idx=0;
while((idx=temp.indexOf(Integer.toString (grid[x][y]),idx))!=-1)
{idx+=1;count+=1;}
return count==3;
}
public static void print(int[][] grid) {
System.out.println();
for(int i=0;i<9;i+=1) {
for (int j=0;j<9;j+=1) {
System.out.print(grid[i][j]);
}
System.out.println();
}
}
}
I will, however, add that the answers I received were less than helpful.
