Merge pull request #74 from samara6855/patch-1

Java program to solve Sudoku

JAVA/SudokuSolver,java

@@ -0,0 +1,95 @@
+package Backtracking;
+
+public class SudokuSolver {
+    public static void main(String[] args) {
+        int[][] board = {
+                { 8, 0, 0, 0, 0, 0, 0, 0, 0 },
+                { 0, 0, 3, 6, 0, 0, 0, 0, 0 },
+                { 0, 7, 0, 0, 9, 0, 2, 0, 0 },
+                { 0, 5, 0, 0, 0, 7, 0, 0, 0 },
+                { 0, 0, 0, 0, 4, 5, 7, 0, 0 },
+                { 0, 0, 0, 1, 0, 0, 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 }
+        };
+        if(solve(board)){
+            display(board);
+        }else{
+            System.out.println("Cannot be Solved");
+        }
+    }
+
+    static boolean solve(int[][] board){
+        int n= board.length;
+        int row=-1;
+        int col=-1;
+
+        boolean emptyLeft = true;
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < n; j++) {
+                if(board[i][j]==0){
+                    row=i;
+                    col=j;
+                    emptyLeft =false;
+                }
+            }
+
+            if(emptyLeft==false){
+                break;
+            }
+
+        }
+        if(emptyLeft==true){
+            return true;
+            //sudoku is solved
+        }
+
+        for (int number = 1; number <= 9; number++) {
+            if(isSafe(board,row,col,number)){
+                board[row][col]=number;
+                if(solve(board)){
+                    return true;
+                }else{
+                    board[row][col]=0;
+                }
+            }
+        }
+        return false;
+    }
+
+    private static void display(int[][] board) {
+        for(int[] row:board){
+            for(int num:row){
+                System.out.print(num + " ");
+            }
+            System.out.println();
+        }
+    }
+
+    static boolean isSafe(int[][] board,int row, int col, int num){
+        for (int i = 0; i < board.length ; i++) {
+            if(board[row][i]==num){
+                return false;
+            }
+        }
+        for (int[] nums: board) {
+            if(nums[col]==num){
+                return false;
+            }
+        }
+
+        int sqrt = (int)Math.sqrt(board.length);
+        int rowStart = row - row%sqrt;
+        int colStart = col - col % sqrt;
+
+        for (int r = rowStart; r < rowStart + sqrt ; r++) {
+            for (int c = colStart; c < colStart + sqrt ; c++) {
+                if(board[r][c]==num){
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+}