1 files changed, 91 insertions, 0 deletions
diff --git a/advent-of-code/2022/09/1.c b/advent-of-code/2022/09/1.c
new file mode 100644
index 0000000..e23a089
--- /dev/null
+++ b/advent-of-code/2022/09/1.c
@@ -0,0 +1,91 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <htable.h>
+#include <crc32.h>
+
+typedef struct {
+    int x;
+    int y;
+} Point;
+
+uint32_t point_hash(void *point) {
+    return crc32(0, point, sizeof(Point));
+}
+
+bool point_eq(void *x, void *y) {
+    Point *a = x, *b = y;
+    return (a->x == b->x) && (a->y == b->y);
+}
+
+typedef struct {
+    Point head;
+    Point tail;
+} State;
+
+bool is_adjacent(Point p1, Point p2) {
+    if (abs(p1.x - p2.x) <= 1 && abs(p2.y - p1.y) <= 1) {
+        return true;
+    }
+    return false;
+}
+
+void run_impl(State *s, HTable *record, int dx, int dy) {
+    Point new = {s->head.x + dx, s->head.y + dy};
+    if (!is_adjacent(s->tail, new)) {
+        s->tail = s->head;
+        htable_insert(record , &(s->tail));
+    }
+    s->head = new;
+}
+
+void run(State *s, HTable *record, char direction, int step) {
+    int dx, dy;
+    switch (direction) {
+        case 'U':
+            dx = 0; dy = 1;
+            break;
+        case 'D':
+            dx = 0; dy = -1;
+            break;
+        case 'L':
+            dx = -1; dy = 0;
+            break;
+        case 'R':
+            dx = 1; dy = 0;
+            break;
+        default:
+            return;
+    }
+    for (int i = 0; i < step; i++) {
+        run_impl(s, record, dx, dy);
+    }
+}
+
+int count_htable(HTable *ht) {
+    int count = 0;
+    for (void *iter = htable_begin(ht);
+            iter != NULL;
+            iter = htable_next(ht, iter)) {
+        count++;
+    }
+    return count;
+}
+
+int main() {
+    FILE *fp = fopen("input", "r");
+    State state;
+    state.head = (Point){0, 0};
+    state.tail = (Point){0, 0};
+    char direction;
+    int step;
+    HTable record;
+    htable_init(&record, sizeof(Point), -1, point_hash, point_eq);
+    while (fscanf(fp, "%c %d", &direction, &step) != EOF) {
+        run(&state, &record, direction, step);
+    }
+    int count = count_htable(&record);
+    printf("%d\n", count);
+    return 0;
+}
+