1 files changed, 69 insertions, 0 deletions
diff --git a/euler90.c b/euler90.c
new file mode 100644
index 0000000..b514269
--- /dev/null
+++ b/euler90.c
@@ -0,0 +1,69 @@
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+char dices[210][6];
+
+#define FOR(i) for (a[i] = a[i-1]+1; a[i] < 10; a[i]++)
+
+void init()
+{
+	char a[6];
+	int k = 0;
+	for (a[0] = 0; a[0] < 10; a[0]++) {
+		FOR(1) {
+			FOR(2) {
+				FOR(3) {
+					FOR(4) {
+						FOR(5) {
+							memcpy(dices[k], a, sizeof(a));
+							k++;
+						}
+					}
+				}
+			}
+		}
+	}
+	assert(k == 210);
+}
+
+int matches(char c, char dic[])
+{
+	for (int i = 0; i < 6; i++) {
+		if (c == dic[i] ||
+				((c == 6 || c== 9) && (dic[i] == 6 || dic[i] == 9)))
+			return 1;
+	}
+	return 0;
+}
+
+int ok(int x, int y)
+{
+	const char sqrs[9][2] = {
+		{0, 1}, {0, 4}, {0, 9}, {1, 6}, {2, 5}, {3, 6}, {4, 9},
+		{6, 4}, {8, 1}
+	};
+	for (int i = 0; i < 9; i++) {
+		if (matches(sqrs[i][0], dices[x])
+				&& matches(sqrs[i][1], dices[y]))
+			continue;
+		if (matches(sqrs[i][0], dices[y])
+				&& matches(sqrs[i][1], dices[x]))
+			continue;
+		return 0;
+	}
+	return 1;
+}
+
+int main()
+{
+	int count = 0;
+	init();
+	for (int i = 0; i < 210; i++) {
+		for (int j = i+1; j < 210; j++) {
+			if (ok(i, j))
+				count++;
+		}
+	}
+	printf("%d\n", count);
+}