sudoku puzzle

Author: ajay1079

SudokuPuzzle.java

@@ -0,0 +1,174 @@
+public class SudokuPuzzle  
+{  
+public boolean isSafe(int[][] b, int r, int c, int n)  
+{  
+// the loop takes care of the clash in the row of the grid  
+for (int d = 0; d < b.length; d++)  
+{  
+  
+// if the number that we have inserted is already   
+// present in that row then return false  
+if (b[r][d] == n)   
+{  
+return false;  
+}  
+}  
+  
+// the loop takes care of the clash in the column of the grid  
+for (int r1 = 0; r1 < b.length; r1++)  
+{  
+  
+// if the number that we have inserted is already   
+// present in that column then return false  
+if (b[r1][c] == n)  
+{  
+return false;  
+}  
+}  
+  
+// the loop takes care of the clash in the sub-grid that is present in the grid  
+int sqt = (int)Math.sqrt(b.length);  
+int boxRowSt = r - r % sqt;  
+int boxColSt = c - c % sqt;  
+  
+for (int r1 = boxRowSt; r1 < boxRowSt + sqt; r1++)  
+{  
+for (int d = boxColSt; d < boxColSt + sqt; d++)  
+{  
+// if the number that we have inserted is already   
+// present in that sub-grid then return false  
+if (b[r1][d] == n)  
+{  
+return false;  
+}  
+}  
+}  
+  
+// if there is no clash in the grid, then it is safe and   
+// true is returned  
+return true;  
+}  
+  
+public boolean solveSudoku(int[][] b, int num)  
+{  
+int r = -1;  
+int c = -1;  
+boolean isVacant = true;  
+for (int i = 0; i < num; i++)  
+{  
+for (int j = 0; j < num; j++)  
+{  
+if (b[i][j] == 0)  
+{  
+r = i;  
+c = j;  
+  
+// false value means   
+// there is still some   
+// vacant cells in the grid  
+isVacant = false;  
+break;  
+}  
+}  
+  
+if (!isVacant)   
+{  
+break;  
+}  
+}  
+  
+// there is no empty space left  
+// in the grid  
+if (isVacant)  
+{  
+return true;  
+}  
+  
+// otherwise for each row do the backtracking  
+for (int no = 1; no <= num; no++)  
+{  
+if (isSafe(b, r, c, no))  
+{  
+b[r][c] = no;  
+if (solveSudoku(b, num))  
+{  
+// display(board, num);  
+return true;  
+}  
+else  
+{  
+  
+b[r][c] = 0;  
+}  
+}  
+}  
+return false;  
+}  
+  
+public void display(int[][] b, int n)  
+{  
+  
+// We have got the solution, just display it  
+for (int i = 0; i < n; i++)  
+{  
+for (int d = 0; d < n; d++)  
+{  
+System.out.print(b[i][d]);  
+System.out.print(" ");  
+}  
+  
+System.out.print("\n");  
+  
+if ((i + 1) % (int)Math.sqrt(n) == 0)  
+{  
+System.out.print("");  
+}  
+}  
+}  
+  
+// main method  
+public static void main(String argvs[])  
+{  
+  
+// the 9 x 9  grid   
+int[][] b = new int[][] { { 7, 0, 0, 0, 0, 0, 2, 0, 0 },   
+                                        { 4, 0, 2, 0, 0, 0, 0, 0, 3 },   
+                                        { 0, 0, 0, 2, 0, 1, 0, 0, 0 },   
+                                        { 3, 0, 0, 1, 8, 0, 0, 9, 7 },   
+                                        { 0, 0, 9, 0, 7, 0, 6, 0, 0 },   
+                                        { 6, 5, 0, 0, 3, 2, 0, 0, 1 },   
+                                        { 0, 0, 0, 4, 0, 9, 0, 0, 0 },   
+                                        { 5, 0, 0, 0, 0, 0, 1, 0, 6 },   
+                                        { 0, 0, 6, 0, 0, 0, 0, 0, 8 }   
+                                     } ;  
+  
+// creating an object of the class SudokuPuzzle  
+SudokuPuzzle obj = new SudokuPuzzle();  
+  
+// computing the size of the grid  
+int size = b.length;  
+  
+System.out.println("The grid is: ");  
+for(int i = 0; i < size; i++)  
+{  
+for(int j = 0; j < size; j++)  
+{  
+System.out.print(b[i][j] + " ");    
+}  
+  
+System.out.println();  
+}  
+System.out.println();  
+if (obj.solveSudoku(b, size))  
+{  
+// display solution  
+  
+System.out.println("The solution of the grid is: ");  
+obj.display(b, size);  
+}  
+else   
+{  
+System.out.println("There is no solution available.");  
+}  
+}  
+}