tasks a-s

Task/N-queens-problem/D/n-queens-problem-1.d

@@ -0,0 +1,44 @@
+import std.stdio;
+
+enum int SIDE = 8;
+int[SIDE] board;
+
+bool unsafe(in int y) nothrow {
+    immutable int x = board[y];
+    foreach (i; 1 .. y + 1) {
+        int t = board[y - i];
+        if ((t == x) || (t == x - i) || (t == x + i))
+            return true;
+    }
+
+    return false;
+}
+
+void showBoard() {
+    static int s = 1;
+    writeln("\nSolution #", s++);
+    foreach (y; 0 .. SIDE) {
+        foreach (x; 0 .. SIDE)
+            write(board[y] == x ? '*' : '.');
+        writeln();
+    }
+}
+
+void main() {
+    int y = 0;
+    board[0] = -1;
+
+    while (y >= 0) {
+        do {
+            board[y]++;
+        } while (board[y] < SIDE && unsafe(y));
+
+        if (board[y] < SIDE) {
+            if (y < (SIDE - 1))
+                board[++y] = -1;
+            else
+                showBoard();
+        } else
+            y--;
+    }
+}