tasks a-s

Task/N-queens-problem/C/n-queens-problem-2.c

@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+typedef uint32_t uint;
+uint full, *qs, count = 0, nn;
+
+void solve(uint d, uint c, uint l, uint r)
+{
+	uint b, a, *s;
+	if (!d) {
+		count++;
+#if 0
+		printf("\nNo. %d\n===========\n", count);
+		for (a = 0; a < nn; a++, putchar('\n'))
+			for (b = 0; b < nn; b++, putchar(' '))
+				putchar(" -QQ"[((b == qs[a])<<1)|((a + b)&1)]);
+#endif
+		return;
+	}
+
+	a = (c | (l <<= 1) | (r >>= 1)) & full;
+	if (a != full)
+		for (*(s = qs + --d) = 0, b = 1; b <= full; (*s)++, b <<= 1)
+			if (!(b & a)) solve(d, b|c, b|l, b|r);
+}
+
+int main(int n, char **argv)
+{
+	if (n <= 1 || (nn = atoi(argv[1])) <= 0) nn = 8;
+
+	qs = calloc(nn, sizeof(int));
+	full = (1U << nn) - 1;
+
+	solve(nn, 0, 0, 0);
+	printf("\nSolutions: %d\n", count);
+	return 0;
+}