postfix chain

demo/queen.c

@@ -0,0 +1,47 @@
+int printf(const char format[], ...);
+int putchar(int ch);
+
+int a[9];
+
+void output() {
+    for (int i = 1; i <= 8; ++i) {
+        for (int j = 1; j <= 8; ++j) {
+            if (a[i] == j) {
+                putchar('x');
+            } else {
+                putchar('-');
+            }
+        }
+        putchar('\n');
+    }
+    putchar('\n');
+}
+
+int ok(int x, int y) {
+    for (int i = 1; i <= x - 1; ++i) {
+        if (a[i] == y || a[i] - i == y - x || a[i] + i == y + x) {
+            return 0;
+        }
+    }
+    return 1;
+}
+
+void queen(int x) {
+    if (x > 8) {
+        output();
+        a[0]++;
+    }
+    for (int y = 1; y <= 8; ++y) {
+        if (ok(x, y)) {
+            a[x] = y;
+            queen(x + 1);
+            a[x] = 0;
+        }
+    }
+}
+
+int main() {
+    queen(1);
+    printf("solutions: %d\n", a[0]);
+    return 0;
+}