2016 Update

Task/Solve-a-Holy-Knights-tour/Java/solve-a-holy-knights-tour.java

@@ -0,0 +1,104 @@
+import java.util.*;
+
+public class HolyKnightsTour {
+
+    final static String[] board = {
+        " xxx    ",
+        " x xx   ",
+        " xxxxxxx",
+        "xxx  x x",
+        "x x  xxx",
+        "1xxxxxx ",
+        "  xx x  ",
+        "   xxx  "};
+
+    private final static int base = 12;
+    private final static int[][] moves = {{1, -2}, {2, -1}, {2, 1}, {1, 2},
+    {-1, 2}, {-2, 1}, {-2, -1}, {-1, -2}};
+    private static int[][] grid;
+    private static int total = 2;
+
+    public static void main(String[] args) {
+        int row = 0, col = 0;
+
+        grid = new int[base][base];
+
+        for (int r = 0; r < base; r++) {
+            Arrays.fill(grid[r], -1);
+            for (int c = 2; c < base - 2; c++) {
+                if (r >= 2 && r < base - 2) {
+                    if (board[r - 2].charAt(c - 2) == 'x') {
+                        grid[r][c] = 0;
+                        total++;
+                    }
+                    if (board[r - 2].charAt(c - 2) == '1') {
+                        row = r;
+                        col = c;
+                    }
+                }
+            }
+        }
+
+        grid[row][col] = 1;
+
+        if (solve(row, col, 2))
+            printResult();
+    }
+
+    private static boolean solve(int r, int c, int count) {
+        if (count == total)
+            return true;
+
+        List<int[]> nbrs = neighbors(r, c);
+
+        if (nbrs.isEmpty() && count != total)
+            return false;
+
+        Collections.sort(nbrs, (a, b) -> a[2] - b[2]);
+
+        for (int[] nb : nbrs) {
+            r = nb[0];
+            c = nb[1];
+            grid[r][c] = count;
+            if (solve(r, c, count + 1))
+                return true;
+            grid[r][c] = 0;
+        }
+
+        return false;
+    }
+
+    private static List<int[]> neighbors(int r, int c) {
+        List<int[]> nbrs = new ArrayList<>();
+
+        for (int[] m : moves) {
+            int x = m[0];
+            int y = m[1];
+            if (grid[r + y][c + x] == 0) {
+                int num = countNeighbors(r + y, c + x) - 1;
+                nbrs.add(new int[]{r + y, c + x, num});
+            }
+        }
+        return nbrs;
+    }
+
+    private static int countNeighbors(int r, int c) {
+        int num = 0;
+        for (int[] m : moves)
+            if (grid[r + m[1]][c + m[0]] == 0)
+                num++;
+        return num;
+    }
+
+    private static void printResult() {
+        for (int[] row : grid) {
+            for (int i : row) {
+                if (i == -1)
+                    System.out.printf("%2s ", ' ');
+                else
+                    System.out.printf("%2d ", i);
+            }
+            System.out.println();
+        }
+    }
+}