1 files changed, 60 insertions, 0 deletions
diff --git a/2020/day07.c b/2020/day07.c
new file mode 100644
index 0000000..3d97d5f
--- /dev/null
+++ b/2020/day07.c
@@ -0,0 +1,60 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+static struct Bag {
+	char adj[16];
+	char col[16];
+	struct {
+		int cnt;
+		char adj[16];
+		char col[16];
+	} cons[4];
+} bags[600];
+static int len;
+static int compar(const void *_a, const void *_b) {
+	const struct Bag *a = _a;
+	const struct Bag *b = _b;
+	int ret = strcmp(a->adj, b->adj);
+	if (ret) return ret;
+	return strcmp(a->col, b->col);
+}
+static struct Bag *findBag(const char *adj, const char *col) {
+	struct Bag needle = {0};
+	strcpy(needle.adj, adj);
+	strcpy(needle.col, col);
+	return bsearch(&needle, bags, len, sizeof(bags[0]), compar);
+}
+static bool canContain(struct Bag *bag, const char *adj, const char *col) {
+	for (int i = 0; i < 4; ++i) {
+		if (!bag->cons[i].adj[0]) break;
+		if (!strcmp(bag->cons[i].adj, adj) && !strcmp(bag->cons[i].col, col)) {
+			return true;
+		}
+		if (canContain(findBag(bag->cons[i].adj, bag->cons[i].col), adj, col)) {
+			return true;
+		}
+	}
+	return false;
+}
+int main(void) {
+	while (EOF != scanf("%s %s bags contain", bags[len].adj, bags[len].col)) {
+		for (
+			int i = 0;
+			0 < scanf(
+				"%d %s %s bag%*[s,.]",
+				&bags[len].cons[i].cnt,
+				bags[len].cons[i].adj, bags[len].cons[i].col
+			);
+			++i
+		);
+		scanf("no other bags.");
+		len++;
+	}
+	qsort(bags, len, sizeof(bags[0]), compar);
+	int count = 0;
+	for (int i = 0; i < len; ++i) {
+		if (canContain(&bags[i], "shiny", "gold")) count++;
+	}
+	printf("%d\n", count);
+}