Data commit

Task/Sudoku/Java/sudoku.java

@@ -0,0 +1,119 @@
+public class Sudoku
+{
+    private int mBoard[][];
+    private int mBoardSize;
+    private int mBoxSize;
+    private boolean mRowSubset[][];
+    private boolean mColSubset[][];
+    private boolean mBoxSubset[][];
+
+    public Sudoku(int board[][]) {
+        mBoard = board;
+        mBoardSize = mBoard.length;
+        mBoxSize = (int)Math.sqrt(mBoardSize);
+        initSubsets();
+    }
+
+    public void initSubsets() {
+        mRowSubset = new boolean[mBoardSize][mBoardSize];
+        mColSubset = new boolean[mBoardSize][mBoardSize];
+        mBoxSubset = new boolean[mBoardSize][mBoardSize];
+        for(int i = 0; i < mBoard.length; i++) {
+            for(int j = 0; j < mBoard.length; j++) {
+                int value = mBoard[i][j];
+                if(value != 0) {
+                    setSubsetValue(i, j, value, true);
+                }
+            }
+        }
+    }
+
+    private void setSubsetValue(int i, int j, int value, boolean present) {
+        mRowSubset[i][value - 1] = present;
+        mColSubset[j][value - 1] = present;
+        mBoxSubset[computeBoxNo(i, j)][value - 1] = present;
+    }
+
+    public boolean solve() {
+        return solve(0, 0);
+    }
+
+    public boolean solve(int i, int j) {
+        if(i == mBoardSize) {
+            i = 0;
+            if(++j == mBoardSize) {
+                return true;
+            }
+        }
+        if(mBoard[i][j] != 0) {
+            return solve(i + 1, j);
+        }
+        for(int value = 1; value <= mBoardSize; value++) {
+            if(isValid(i, j, value)) {
+                mBoard[i][j] = value;
+                setSubsetValue(i, j, value, true);
+                if(solve(i + 1, j)) {
+                    return true;
+                }
+                setSubsetValue(i, j, value, false);
+            }
+        }
+
+        mBoard[i][j] = 0;
+        return false;
+    }
+
+    private boolean isValid(int i, int j, int val) {
+        val--;
+        boolean isPresent = mRowSubset[i][val] || mColSubset[j][val] || mBoxSubset[computeBoxNo(i, j)][val];
+        return !isPresent;
+    }
+
+    private int computeBoxNo(int i, int j) {
+        int boxRow = i / mBoxSize;
+        int boxCol = j / mBoxSize;
+        return boxRow * mBoxSize + boxCol;
+    }
+
+    public void print() {
+        for(int i = 0; i < mBoardSize; i++) {
+            if(i % mBoxSize == 0) {
+                System.out.println(" -----------------------");
+            }
+            for(int j = 0; j < mBoardSize; j++) {
+                if(j % mBoxSize == 0) {
+                    System.out.print("| ");
+                }
+                System.out.print(mBoard[i][j] != 0 ? ((Object) (Integer.valueOf(mBoard[i][j]))) : "-");
+                System.out.print(' ');
+            }
+
+            System.out.println("|");
+        }
+
+        System.out.println(" -----------------------");
+    }
+
+    public static void main(String[] args) {
+        int[][] board = {
+            {8, 5, 0, 0, 0, 2, 4, 0, 0},
+            {7, 2, 0, 0, 0, 0, 0, 0, 9},
+            {0, 0, 4, 0, 0, 0, 0, 0, 0},
+            {0, 0, 0, 1, 0, 7, 0, 0, 2},
+            {3, 0, 5, 0, 0, 0, 9, 0, 0},
+            {0, 4, 0, 0, 0, 0, 0, 0, 0},
+            {0, 0, 0, 0, 8, 0, 0, 7, 0},
+            {0, 1, 7, 0, 0, 0, 0, 0, 0},
+            {0, 0, 0, 0, 3, 6, 0, 4, 0}
+        };
+        Sudoku s = new Sudoku(board);
+        System.out.print("Starting grid:\n");
+        s.print();
+        if (s.solve()) {
+            System.out.print("\nSolution:\n");
+            s.print();
+        } else {
+            System.out.println("\nUnsolvable!");
+        }
+    }
+}