day9p2

day9p2/Makefile

@@ -0,0 +1,12 @@
+CFLAGS := -Wall -Wextra -std=c17 -D_GNU_SOURCE
+
+#LIBS := glib-2.0
+#CFLAGS += $(shell pkg-config --cflags $(LIBS))
+#LDLIBS := $(shell pkg-config --libs $(LIBS))
+
+.PHONY: all
+all: main
+
+.PHONY: clean
+clean:
+	rm -f main

day9p2/input

@@ -0,0 +1 @@
+447 players; last marble is worth 71510 points

day9p2/main.c

@@ -0,0 +1,89 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+struct marble {
+    struct marble *next;
+    struct marble *prev;
+    int value;
+};
+
+void *xmalloc(size_t size)
+{
+    void *res = malloc(size);
+    if (!res) {
+        perror("malloc");
+        exit(1);
+    }
+    return res;
+}
+
+void *xcalloc(size_t nmemb, size_t size)
+{
+    void *res = calloc(nmemb, size);
+    if (!res) {
+        perror("calloc");
+        exit(1);
+    }
+    return res;
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc <= 2) {
+        fprintf(stderr, "Usage: %s <players> <marbles>\n", argv[0]);
+        return 1;
+    }
+
+    int players = strtol(argv[1], NULL, 0);
+    int marbles = strtol(argv[2], NULL, 0) * 100;
+    if (!players || marbles <= 1) return 1;
+
+    unsigned *scores = xcalloc(players, sizeof(unsigned));
+    int player = 0;
+
+    struct marble *current = xmalloc(sizeof(struct marble));
+    current->next = current;
+    current->prev = current;
+    current->value = 0;
+
+    for (int i = 1; i <= marbles; i++) {
+        if (i % 23 == 0) {
+            scores[player] += i;
+            for (int i = 0; i < 7; i++) {
+                current = current->prev;
+            }
+            scores[player] += current->value;
+            current->prev->next = current->next;
+            current->next->prev = current->prev;
+
+            struct marble *remove = current;
+            current = current->next;
+            free(remove);
+        } else {
+            current = current->next;
+            struct marble *new = xmalloc(sizeof(struct marble));
+            new->next = current->next;
+            new->prev = current;
+            new->next->prev = new;
+            new->prev->next = new;
+            new->value = i;
+            current = new;
+        }
+
+        if (++player >= players) player = 0;
+    }
+
+    unsigned highest = 0;
+    for (unsigned *score = scores; score < scores + players; score++) {
+        if (*score > highest) highest = *score;
+    }
+    printf("Highest score: %u\n", highest);
+
+    current->prev->next = NULL;
+    while (current->next) {
+        current = current->next;
+        free(current->prev);
+    }
+    free(current);
+    return 0;
+}