nqueens

README

@@ -3,4 +3,5 @@ for details/demos/screenshots.
 
 - asm: simple assembly program that slides a three-digit number across the
   terminal and an external seven-segment display.
+- nqueens: n-queens solver and graphical display.
 - tablut: ANSI C / ncurses implementation of the game Tablut.

nqueens/Makefile

+all: nqueens/NQueens.class
+
+.PHONY: clean
+clean:
+	rm -f nqueens/*.class
+
+%.class: %.java
+	javac $<
+
+nqueens/NQueens.class: nqueens/NQueens.java
+nqueens/NQueens.java: \
+	nqueens/Solver.java nqueens/Solver.class \
+	nqueens/Window.java nqueens/Window.class
+nqueens/Solver.java: nqueens/Window.java nqueens/Window.class

nqueens/nqueens/NQueens.java

+package nqueens;
+
+import java.util.ArrayList;
+import java.util.List;
+import javax.swing.JOptionPane;
+
+public class NQueens {
+    public static void main(String[] args) {
+        String n_str = JOptionPane.showInputDialog("n:");
+        if(n_str == null)
+            return;
+        int n = Integer.parseInt(n_str);
+        Solver s = new Solver(n);
+        List<char[][]> l = new ArrayList<char[][]>();
+        for(int i = 0; i < n; i++)
+            s.nqueen(0, i, l);
+        Window w = new Window();
+        w.set_solutions(l);
+        w.revalidate();
+        w.repaint();
+        w.pack();
+    }
+}

nqueens/nqueens/Solver.java

+package nqueens;
+
+import java.util.List;
+
+public class Solver {
+    int l, c;
+    char[][] mat;
+
+    public Solver(int n) {
+        this.l = 0;
+        this.c = 0;
+        this.mat = this.create_matrix(n);
+    }
+
+    public int nqueen(int l, int c, List<char[][]> r) {
+        int n = this.mat.length;
+        if(this.possible(this.mat, l, c)) {
+            this.mat[l][c] = 'q';
+            if(l == n - 1) {
+                r.add(this.dup_mat(this.mat));
+                this.mat[l][c] = 0;
+                return 1;
+            } else {
+                int np = 0;
+                for(int i = 0; i < n; i++) {
+                    np += nqueen(l + 1, i, r);
+                }
+                this.mat[l][c] = 0;
+                return np;
+            }
+        }
+        return 0;
+    }
+
+    public static char[][] create_matrix(int n) {
+        char[][] m = new char[n][n];
+        for(int i = 0; i < n; i++)
+            for(int j = 0; j < n; j++)
+                m[i][j] = 0;
+        return m;
+    }
+
+    private static char[][] dup_mat(char[][] m) {
+        int n = m.length;
+        char[][] mat_dup = new char[n][n];
+        for(int i = 0; i < n; ++i)
+            for(int j = 0; j < n; ++j)
+                mat_dup[i][j] = m[i][j];
+        return mat_dup;
+    }
+
+    private static boolean possible(char[][] m, int l, int c) {
+        if(l == 0)
+            return true;
+        int i, j;
+        for(i = 0; i < l; i++)
+            if(m[i][c] != 0)
+                return false;
+        i = l - 1;
+        j = c - 1;
+        while(i >= 0 && j >= 0) {
+            if(m[i][j] != 0)
+                return false;
+            i--;
+            j--;
+        }
+        i = l - 1;
+        j = c + 1;
+        while(i >= 0 && j < m.length) {
+            if(m[i][j] != 0)
+                return false;
+            i--;
+            j++;
+        }
+        return true;
+    }
+}

nqueens/nqueens/Window.java

+package nqueens;
+
+import java.awt.Color;
+import java.awt.Dimension;
+import java.awt.GridLayout;
+import java.awt.Graphics;
+import java.util.List;
+import javax.swing.JFrame;
+import javax.swing.JPanel;
+import javax.swing.JScrollPane;
+import javax.swing.ScrollPaneConstants;
+
+public class Window extends JFrame {
+    private static final long serialVersionUID = 1L;
+    private final int TAM = 50;
+
+    public Window() {
+        super();
+        setDefaultCloseOperation(EXIT_ON_CLOSE);
+        setSize(new Dimension(800, 600));
+        setVisible(true);
+    }
+
+    public void set_solutions(List<char[][]> r) {
+        final int n = (int)Math.floor(Math.sqrt(r.size()));
+        JPanel p = new JPanel(new GridLayout(n, n));
+        for(char[][] m : r) {
+            JPanel new_panel = new JPanel();
+            new_panel.add(new Display(m));
+            p.add(new_panel);
+        }
+        setContentPane(new JScrollPane(p));
+    }
+
+    private class Display extends JPanel {
+        private static final long serialVersionUID = 1L;
+        char[][] mat;
+
+        public Display(char[][] mat) {
+            super();
+            this.mat = mat;
+            this.setBackground(Color.WHITE);
+            Dimension d = new Dimension(
+                mat.length * TAM + 1, mat.length * TAM + 1);
+            this.setSize(d);
+            this.setPreferredSize(d);
+            this.setMinimumSize(d);
+            this.setMaximumSize(d);
+        }
+
+        public void paintComponent(Graphics g) {
+            super.paintComponent(g);
+            int n = this.mat.length;
+            for(int i = 0; i <= n; i++) {
+                g.drawLine(0, i * TAM, n * TAM, i * TAM);
+                g.drawLine(i * TAM, 0, i * TAM, n * TAM);
+            }
+            for(int i = 0; i < n; i++)
+                for(int j = 0; j < n; j++)
+                    if(this.mat[i][j] == 'q')
+                        g.drawString(
+                            "q",
+                            (j + 1) * TAM - TAM / 2,
+                            (i + 1) * TAM - TAM / 2);
+        }
+    }
+}