Data commit

Task/Peaceful-chess-queen-armies/Java/peaceful-chess-queen-armies.java

@@ -0,0 +1,148 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Peaceful {
+    enum Piece {
+        Empty,
+        Black,
+        White,
+    }
+
+    public static class Position {
+        public int x, y;
+
+        public Position(int x, int y) {
+            this.x = x;
+            this.y = y;
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (obj instanceof Position) {
+                Position pos = (Position) obj;
+                return pos.x == x && pos.y == y;
+            }
+            return false;
+        }
+    }
+
+    private static boolean place(int m, int n, List<Position> pBlackQueens, List<Position> pWhiteQueens) {
+        if (m == 0) {
+            return true;
+        }
+        boolean placingBlack = true;
+        for (int i = 0; i < n; ++i) {
+            inner:
+            for (int j = 0; j < n; ++j) {
+                Position pos = new Position(i, j);
+                for (Position queen : pBlackQueens) {
+                    if (pos.equals(queen) || !placingBlack && isAttacking(queen, pos)) {
+                        continue inner;
+                    }
+                }
+                for (Position queen : pWhiteQueens) {
+                    if (pos.equals(queen) || placingBlack && isAttacking(queen, pos)) {
+                        continue inner;
+                    }
+                }
+                if (placingBlack) {
+                    pBlackQueens.add(pos);
+                    placingBlack = false;
+                } else {
+                    pWhiteQueens.add(pos);
+                    if (place(m - 1, n, pBlackQueens, pWhiteQueens)) {
+                        return true;
+                    }
+                    pBlackQueens.remove(pBlackQueens.size() - 1);
+                    pWhiteQueens.remove(pWhiteQueens.size() - 1);
+                    placingBlack = true;
+                }
+            }
+        }
+        if (!placingBlack) {
+            pBlackQueens.remove(pBlackQueens.size() - 1);
+        }
+        return false;
+    }
+
+    private static boolean isAttacking(Position queen, Position pos) {
+        return queen.x == pos.x
+            || queen.y == pos.y
+            || Math.abs(queen.x - pos.x) == Math.abs(queen.y - pos.y);
+    }
+
+    private static void printBoard(int n, List<Position> blackQueens, List<Position> whiteQueens) {
+        Piece[] board = new Piece[n * n];
+        Arrays.fill(board, Piece.Empty);
+
+        for (Position queen : blackQueens) {
+            board[queen.x + n * queen.y] = Piece.Black;
+        }
+        for (Position queen : whiteQueens) {
+            board[queen.x + n * queen.y] = Piece.White;
+        }
+        for (int i = 0; i < board.length; ++i) {
+            if ((i != 0) && i % n == 0) {
+                System.out.println();
+            }
+
+            Piece b = board[i];
+            if (b == Piece.Black) {
+                System.out.print("B ");
+            } else if (b == Piece.White) {
+                System.out.print("W ");
+            } else {
+                int j = i / n;
+                int k = i - j * n;
+                if (j % 2 == k % 2) {
+                    System.out.print("• ");
+                } else {
+                    System.out.print("◦ ");
+                }
+            }
+        }
+        System.out.println('\n');
+    }
+
+    public static void main(String[] args) {
+        List<Position> nms = List.of(
+            new Position(2, 1),
+            new Position(3, 1),
+            new Position(3, 2),
+            new Position(4, 1),
+            new Position(4, 2),
+            new Position(4, 3),
+            new Position(5, 1),
+            new Position(5, 2),
+            new Position(5, 3),
+            new Position(5, 4),
+            new Position(5, 5),
+            new Position(6, 1),
+            new Position(6, 2),
+            new Position(6, 3),
+            new Position(6, 4),
+            new Position(6, 5),
+            new Position(6, 6),
+            new Position(7, 1),
+            new Position(7, 2),
+            new Position(7, 3),
+            new Position(7, 4),
+            new Position(7, 5),
+            new Position(7, 6),
+            new Position(7, 7)
+        );
+        for (Position nm : nms) {
+            int m = nm.y;
+            int n = nm.x;
+            System.out.printf("%d black and %d white queens on a %d x %d board:\n", m, m, n, n);
+            List<Position> blackQueens = new ArrayList<>();
+            List<Position> whiteQueens = new ArrayList<>();
+            if (place(m, n, blackQueens, whiteQueens)) {
+                printBoard(n, blackQueens, whiteQueens);
+            } else {
+                System.out.println("No solution exists.\n");
+            }
+        }
+    }
+}